diff --git a/.changesets/fix_rohan_b99_missing_metrics_including_response_body_size.md b/.changesets/fix_rohan_b99_missing_metrics_including_response_body_size.md
new file mode 100644
index 0000000000..885c75cc45
--- /dev/null
+++ b/.changesets/fix_rohan_b99_missing_metrics_including_response_body_size.md
@@ -0,0 +1,5 @@
+### Ensure `http.server.response.body.size` metric is recorded ([PR #8697](https://github.com/apollographql/router/pull/8697))
+
+Previously, the `http.server.response.body.size` metric was not recorded as we attempted to read from the `Content-Length` header of the response before it had been set. We now use the `size_hint` of the body if it is exact.
+
+By [@rohan-b99](https://github.com/rohan-b99) in https://github.com/apollographql/router/pull/8697
diff --git a/apollo-router/src/configuration/snapshots/apollo_router__configuration__tests__schema_generation.snap b/apollo-router/src/configuration/snapshots/apollo_router__configuration__tests__schema_generation.snap
index 86c7cb6816..4d97276df7 100644
--- a/apollo-router/src/configuration/snapshots/apollo_router__configuration__tests__schema_generation.snap
+++ b/apollo-router/src/configuration/snapshots/apollo_router__configuration__tests__schema_generation.snap
@@ -8332,6 +8332,20 @@ expression: "&schema"
           ],
           "type": "object"
         },
+        {
+          "additionalProperties": false,
+          "description": "The size hint of the body.\nThis is used as the Content-Length header has not yet been populated\nwhen selectors are evaluated",
+          "properties": {
+            "response_size_hint": {
+              "description": "Extract response size hint in bytes",
+              "type": "boolean"
+            }
+          },
+          "required": [
+            "response_size_hint"
+          ],
+          "type": "object"
+        },
         {
           "additionalProperties": false,
           "description": "Router overhead duration (time not spent in subgraph requests)",
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter/router.yaml
index dbecbd4ed6..de2e539154 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom_counter":
           description: "count of requests"
           type: counter
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_custom_value/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_custom_value/router.yaml
index f6a40d1765..e391996dea 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_custom_value/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_custom_value/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom_counter":
           description: "count of requests"
           type: counter
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_attributes/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_attributes/router.yaml
index ae6977491d..5e97dc2c59 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_attributes/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_attributes/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom_counter":
           description: "count of requests"
           type: counter
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_conditions/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_conditions/router.yaml
index 5e1bdc25ca..7db03bc31f 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_conditions/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_counter_with_conditions/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom_counter":
           description: "count of requests"
           type: counter
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_custom_value/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_custom_value/router.yaml
index 74d95b1924..25f6f8c01d 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_custom_value/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_custom_value/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom.histogram":
           description: "histogram of requests"
           type: histogram
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_duration/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_duration/router.yaml
index e1796e90b6..bdc783d789 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_duration/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_duration/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom.histogram.duration":
           description: "histogram of requests"
           type: histogram
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_unit/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_unit/router.yaml
index 813abb4615..59991866a0 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_unit/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_unit/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom.histogram":
           description: "histogram of requests"
           type: histogram
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_attributes/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_attributes/router.yaml
index d37b70d822..841b0b8f0d 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_attributes/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_attributes/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom.histogram":
           description: "histogram of requests"
           type: histogram
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_conditions/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_conditions/router.yaml
index faa6a69a28..f7b1c44838 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_conditions/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/custom_histogram_with_conditions/router.yaml
@@ -4,6 +4,7 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
+        http.server.response.body.size: false
         "custom.histogram":
           description: "histogram of requests"
           type: histogram
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.active_requests/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.active_requests/router.yaml
index e9b3ac1c2d..ae82a62f70 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.active_requests/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.active_requests/router.yaml
@@ -4,5 +4,6 @@ telemetry:
       router:
         http.server.active_requests: true
         http.server.request.duration: false
+        http.server.response.body.size: false
       subgraph:
         http.client.request.duration: false
\ No newline at end of file
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size/router.yaml
index 42455f7354..aaeea5f87c 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size/router.yaml
@@ -4,4 +4,5 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
-        http.server.request.body.size: true
\ No newline at end of file
+        http.server.request.body.size: true
+        http.server.response.body.size: false
\ No newline at end of file
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size_with_custom_attributes/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size_with_custom_attributes/router.yaml
index 42455f7354..aaeea5f87c 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size_with_custom_attributes/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.body.size_with_custom_attributes/router.yaml
@@ -4,4 +4,5 @@ telemetry:
       router:
         http.server.active_requests: false
         http.server.request.duration: false
-        http.server.request.body.size: true
\ No newline at end of file
+        http.server.request.body.size: true
+        http.server.response.body.size: false
\ No newline at end of file
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration/router.yaml
index 5411b485dd..8b117049a2 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration/router.yaml
@@ -3,4 +3,5 @@ telemetry:
     instruments:
       router:
         http.server.active_requests: false
-        http.server.request.duration: true
\ No newline at end of file
+        http.server.request.duration: true
+        http.server.response.body.size: false
\ No newline at end of file
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration_with_custom_attributes/router.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration_with_custom_attributes/router.yaml
index ef8332ead1..941203aec4 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration_with_custom_attributes/router.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.request.duration_with_custom_attributes/router.yaml
@@ -3,6 +3,7 @@ telemetry:
     instruments:
       router:
         http.server.active_requests: false
+        http.server.response.body.size: false
         http.server.request.duration:
           attributes:
             http.request.method:
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/metrics.snap b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/metrics.snap
index 245131f105..0184468d38 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/metrics.snap
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/metrics.snap
@@ -16,7 +16,7 @@ info:
   unit: By
   data:
     datapoints:
-      - sum: 35
+      - sum: 18
         count: 1
         attributes:
           http.request.method: GET
diff --git a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/test.yaml b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/test.yaml
index b0bbb9625a..323075d1fb 100644
--- a/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/test.yaml
+++ b/apollo-router/src/plugins/telemetry/config_new/fixtures/router/http.server.response.body.size/test.yaml
@@ -6,8 +6,6 @@ events:
         body: |
           hello
     - router_response:
-        headers:
-          "content-length": "35"
         body: |
           hello
         status: 200
\ No newline at end of file
diff --git a/apollo-router/src/plugins/telemetry/config_new/instruments.rs b/apollo-router/src/plugins/telemetry/config_new/instruments.rs
index fd4919cf6f..aafe264f96 100644
--- a/apollo-router/src/plugins/telemetry/config_new/instruments.rs
+++ b/apollo-router/src/plugins/telemetry/config_new/instruments.rs
@@ -401,11 +401,7 @@ impl InstrumentsConfig {
                                     )
                             ),
                             attributes: Vec::with_capacity(nb_attributes),
-                            selector: Some(Arc::new(RouterSelector::ResponseHeader {
-                                response_header: "content-length".to_string(),
-                                redact: None,
-                                default: None,
-                            })),
+                            selector: Some(Arc::new(RouterSelector::ResponseSizeHint { response_size_hint: true })),
                             selectors,
                             updated: false,
                             _phantom: PhantomData,
@@ -3463,7 +3459,6 @@ mod tests {
                 .status_code(StatusCode::BAD_REQUEST)
                 .header("content-type", "application/json")
                 .header("x-my-header", "TEST")
-                .header("content-length", "35")
                 .data(json!({"errors": [{"message": "nope"}]}))
                 .build()
                 .unwrap();
@@ -3483,7 +3478,7 @@ mod tests {
             assert_histogram_sum!("http.server.request.body.size", 35.0);
             assert_histogram_sum!(
                 "http.server.response.body.size",
-                35.0,
+                40.0,
                 "acme.my_attribute" = "TEST"
             );
 
@@ -3500,7 +3495,6 @@ mod tests {
                 .context(router_req.context.clone())
                 .status_code(StatusCode::BAD_REQUEST)
                 .header("content-type", "application/json")
-                .header("content-length", "35")
                 .data(json!({"errors": [{"message": "nope"}]}))
                 .build()
                 .unwrap();
@@ -3520,12 +3514,12 @@ mod tests {
             assert_histogram_sum!("http.server.request.body.size", 70.0);
             assert_histogram_sum!(
                 "http.server.response.body.size",
-                35.0,
+                40.0,
                 "acme.my_attribute" = "TEST"
             );
             assert_histogram_sum!(
                 "http.server.response.body.size",
-                35.0,
+                40.0,
                 "acme.my_attribute" = "unknown"
             );
 
@@ -3541,7 +3535,6 @@ mod tests {
                 .context(router_req.context.clone())
                 .status_code(StatusCode::OK)
                 .header("content-type", "application/json")
-                .header("content-length", "35")
                 .data(json!({"errors": [{"message": "nope"}]}))
                 .build()
                 .unwrap();
diff --git a/apollo-router/src/plugins/telemetry/config_new/router/selectors.rs b/apollo-router/src/plugins/telemetry/config_new/router/selectors.rs
index ecc709e7a8..e2b9f8cee3 100644
--- a/apollo-router/src/plugins/telemetry/config_new/router/selectors.rs
+++ b/apollo-router/src/plugins/telemetry/config_new/router/selectors.rs
@@ -1,4 +1,5 @@
 use derivative::Derivative;
+use http_body::Body;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde_json::from_str;
@@ -159,6 +160,13 @@ pub(crate) enum RouterSelector {
         /// The http response status code.
         response_status: ResponseStatus,
     },
+    /// The size hint of the body.
+    /// This is used as the Content-Length header has not yet been populated
+    /// when selectors are evaluated
+    ResponseSizeHint {
+        /// Extract response size hint in bytes
+        response_size_hint: bool,
+    },
     /// Router overhead duration (time not spent in subgraph requests)
     RouterOverhead {
         /// Extract router overhead duration in seconds
@@ -311,6 +319,13 @@ impl Selector for RouterSelector {
                     .canonical_reason()
                     .map(|reason| reason.to_string().into()),
             },
+            RouterSelector::ResponseSizeHint { response_size_hint } if *response_size_hint => {
+                response
+                    .response
+                    .size_hint()
+                    .exact()
+                    .map(|size| opentelemetry::Value::I64(size as i64))
+            }
             RouterSelector::RouterOverhead { router_overhead } if *router_overhead => response
                 .context
                 .extensions()
@@ -459,6 +474,7 @@ impl Selector for RouterSelector {
                     | RouterSelector::ResponseHeader { .. }
                     | RouterSelector::ResponseContext { .. }
                     | RouterSelector::ResponseStatus { .. }
+                    | RouterSelector::ResponseSizeHint { .. }
                     | RouterSelector::RouterOverhead { .. }
                     | RouterSelector::ActiveSubgraphRequests { .. }
                     | RouterSelector::OnGraphQLError { .. }
@@ -975,6 +991,25 @@ mod test {
         );
     }
 
+    #[test]
+    fn router_response_size_hint() {
+        let selector = RouterSelector::ResponseSizeHint {
+            response_size_hint: true,
+        };
+        assert_eq!(
+            selector
+                .on_response(
+                    &crate::services::RouterResponse::fake_builder()
+                        .data("value")
+                        .build()
+                        .unwrap()
+                )
+                .unwrap(),
+            // The actual response body is {"data":"value"}
+            opentelemetry::Value::I64(16)
+        );
+    }
+
     #[test]
     fn router_response_body() {
         let selector = RouterSelector::ResponseBody {
diff --git a/docs/source/routing/observability/router-telemetry-otel/enabling-telemetry/instruments.mdx b/docs/source/routing/observability/router-telemetry-otel/enabling-telemetry/instruments.mdx
index 0abcc587e9..c0c5d5ab28 100644
--- a/docs/source/routing/observability/router-telemetry-otel/enabling-telemetry/instruments.mdx
+++ b/docs/source/routing/observability/router-telemetry-otel/enabling-telemetry/instruments.mdx
@@ -24,6 +24,7 @@ OpenTelemetry specifies multiple [standard metric instruments](https://opentelem
   * `http.server.active_requests` - The number of active requests in flight.
   * `http.server.request.body.size` - A histogram of request body sizes for requests handled by the router.
   * `http.server.request.duration` - A histogram of request durations for requests handled by the router.
+  * `http.server.response.body.size` - A histogram of response body sizes for requests handled by the router.
 
 + In the [subgraph service](#router-request-lifecycle-services):
 
@@ -53,6 +54,7 @@ telemetry:
         http.server.active_requests: true # (default false)
         http.server.request.body.size: true # (default false)
         http.server.request.duration: true # (default false)
+        http.server.response.body.size: true # (default false)
       subgraph:
         http.client.request.body.size: true # (default false)
         http.client.request.duration: true # (default false)