diff --git a/api.middlewares.go b/api.middlewares.go
index 4d7211f..6fe6f01 100644
--- a/api.middlewares.go
+++ b/api.middlewares.go
@@ -33,14 +33,15 @@ func (api *APIHandler) DurationMiddleware(next httprouter.Handle) httprouter.Han
 		next(nw, r, ps)
 		logger.Info(
 			"stats",
-			zap.Int("request.status", nw.statusCode),
+			zap.Int("request.status", nw.Status()),
+			zap.Int("bytes.sent", nw.Bytes()),
 			zap.Duration("request.duration", api.clock.Now().Sub(start)),
 		)
 		api.stats.mu.Lock()
-		if num, found := api.stats.status[nw.statusCode]; !found {
-			api.stats.status[nw.statusCode] = 1
+		if num, found := api.stats.status[nw.code]; !found {
+			api.stats.status[nw.code] = 1
 		} else {
-			api.stats.status[nw.statusCode] = num + 1
+			api.stats.status[nw.code] = num + 1
 		}
 		api.stats.mu.Unlock()
 	}
diff --git a/helpers.response.go b/helpers.response.go
index 27ec5de..49ddff2 100644
--- a/helpers.response.go
+++ b/helpers.response.go
@@ -5,39 +5,62 @@ import (
 	"net/http"
 )
 
-// CustomResponseWriter is a wrapper for http.ResponseWriter.
-// It is used to record response attributes like statusCode.
+// CustomResponseWriter is a wrapper for http.ResponseWriter. It is
+// used to record response details like status code and body size.
 type CustomResponseWriter struct {
 	http.ResponseWriter
-	statusCode int
+	code  int
+	bytes int
+	wrote bool
 }
 
 // NewCustomResponseWriter provides CustomResponseWriter with 200 as status code.
 func NewCustomResponseWriter(rw http.ResponseWriter) *CustomResponseWriter {
 	return &CustomResponseWriter{
 		ResponseWriter: rw,
-		statusCode:     200,
+		code:           200,
 	}
 }
 
 // Header implements http.Header interface.
-func (rw *CustomResponseWriter) Header() http.Header {
-	return rw.ResponseWriter.Header()
+func (cw *CustomResponseWriter) Header() http.Header {
+	return cw.ResponseWriter.Header()
 }
 
 // WriteHeader implements http.WriteHeader interface.
-func (rw *CustomResponseWriter) WriteHeader(statusCode int) {
-	rw.ResponseWriter.WriteHeader(statusCode)
-	rw.statusCode = statusCode
+func (cw *CustomResponseWriter) WriteHeader(code int) {
+	if !cw.wrote {
+		cw.code = code
+		cw.wrote = true
+		cw.ResponseWriter.WriteHeader(code)
+	}
 }
 
 // Write implements http.Write interface.
-func (rw *CustomResponseWriter) Write(bytes []byte) (int, error) {
-	return rw.ResponseWriter.Write(bytes)
+func (cw *CustomResponseWriter) Write(bytes []byte) (int, error) {
+	if !cw.wrote {
+		cw.WriteHeader(cw.code)
+	}
+
+	n, err := cw.ResponseWriter.Write(bytes)
+	cw.bytes += n
+	return n, err
+}
+
+// Status returns the written status code.
+func (cw *CustomResponseWriter) Status() int {
+	return cw.code
+}
+
+// Bytes returns bytes written as response body.
+func (cw *CustomResponseWriter) Bytes() int {
+	return cw.bytes
 }
 
-func (rw *CustomResponseWriter) Status() int {
-	return rw.statusCode
+// Unwrap returns native response writer and used by
+// the http.ResponseController during its operation.
+func (cw *CustomResponseWriter) Unwrap() http.ResponseWriter {
+	return cw.ResponseWriter
 }
 
 // APIError is the data model sent when an error occurred during request processing.