diff --git a/render/data.go b/render/data.go
index a653ea30..d652a65c 100644
--- a/render/data.go
+++ b/render/data.go
@@ -15,6 +15,9 @@ type Data struct {
 // Render (Data) writes data with custom ContentType.
 func (r Data) Render(w http.ResponseWriter) (err error) {
 	r.WriteContentType(w)
+
+	writeContentLength(w, len(r.Data))
+
 	_, err = w.Write(r.Data)
 	return
 }
diff --git a/render/json.go b/render/json.go
index fc8dea45..78b00f6f 100644
--- a/render/json.go
+++ b/render/json.go
@@ -62,6 +62,11 @@ func (r JSON) WriteContentType(w http.ResponseWriter) {
 	writeContentType(w, jsonContentType)
 }
 
+// WriteContentType (JSON) writes JSON ContentType.
+func (r JSON) WriteContentLength(w http.ResponseWriter, length int) {
+	writeContentLength(w, length)
+}
+
 // WriteJSON marshals the given interface object and writes it with custom ContentType.
 func WriteJSON(w http.ResponseWriter, obj any) error {
 	writeContentType(w, jsonContentType)
@@ -69,6 +74,9 @@ func WriteJSON(w http.ResponseWriter, obj any) error {
 	if err != nil {
 		return err
 	}
+
+	writeContentLength(w, len(jsonBytes))
+
 	_, err = w.Write(jsonBytes)
 	return err
 }
@@ -80,6 +88,9 @@ func (r IndentedJSON) Render(w http.ResponseWriter) error {
 	if err != nil {
 		return err
 	}
+
+	writeContentLength(w, len(jsonBytes))
+
 	_, err = w.Write(jsonBytes)
 	return err
 }
@@ -96,13 +107,22 @@ func (r SecureJSON) Render(w http.ResponseWriter) error {
 	if err != nil {
 		return err
 	}
+
+	length := len(jsonBytes)
+
 	// if the jsonBytes is array values
 	if bytes.HasPrefix(jsonBytes, bytesconv.StringToBytes("[")) && bytes.HasSuffix(jsonBytes,
 		bytesconv.StringToBytes("]")) {
+
 		if _, err = w.Write(bytesconv.StringToBytes(r.Prefix)); err != nil {
 			return err
 		}
+		length += len(r.Prefix)
+
 	}
+
+	writeContentLength(w, length)
+
 	_, err = w.Write(jsonBytes)
 	return err
 }
@@ -115,18 +135,24 @@ func (r SecureJSON) WriteContentType(w http.ResponseWriter) {
 // Render (JsonpJSON) marshals the given interface object and writes it and its callback with custom ContentType.
 func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
 	r.WriteContentType(w)
-	ret, err := json.Marshal(r.Data)
+	jsonBytes, err := json.Marshal(r.Data)
 	if err != nil {
 		return err
 	}
 
+	length := len(jsonBytes)
+
 	if r.Callback == "" {
-		_, err = w.Write(ret)
+		writeContentLength(w, length)
+
+		_, err = w.Write(jsonBytes)
 		return err
 	}
 
 	callback := template.JSEscapeString(r.Callback)
-	if _, err = w.Write(bytesconv.StringToBytes(callback)); err != nil {
+	callbackBytes := bytesconv.StringToBytes(callback)
+
+	if _, err = w.Write(callbackBytes); err != nil {
 		return err
 	}
 
@@ -134,7 +160,7 @@ func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
 		return err
 	}
 
-	if _, err = w.Write(ret); err != nil {
+	if _, err = w.Write(jsonBytes); err != nil {
 		return err
 	}
 
@@ -142,6 +168,10 @@ func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
 		return err
 	}
 
+	length += len(callbackBytes) + 3 // 3 = len("();")
+
+	writeContentLength(w, length)
+
 	return nil
 }
 
@@ -167,7 +197,11 @@ func (r AsciiJSON) Render(w http.ResponseWriter) (err error) {
 		buffer.WriteString(cvt)
 	}
 
-	_, err = w.Write(buffer.Bytes())
+	jsonBytes := buffer.Bytes()
+
+	writeContentLength(w, len(jsonBytes))
+
+	_, err = w.Write(jsonBytes)
 	return err
 }
 
diff --git a/render/protobuf.go b/render/protobuf.go
index 9331c405..b9e78874 100644
--- a/render/protobuf.go
+++ b/render/protobuf.go
@@ -26,6 +26,8 @@ func (r ProtoBuf) Render(w http.ResponseWriter) error {
 		return err
 	}
 
+	writeContentLength(w, len(bytes))
+
 	_, err = w.Write(bytes)
 	return err
 }
diff --git a/render/render.go b/render/render.go
index 7955000c..410994fe 100644
--- a/render/render.go
+++ b/render/render.go
@@ -4,7 +4,10 @@
 
 package render
 
-import "net/http"
+import (
+	"net/http"
+	"strconv"
+)
 
 // Render interface is to be implemented by JSON, XML, HTML, YAML and so on.
 type Render interface {
@@ -39,3 +42,7 @@ func writeContentType(w http.ResponseWriter, value []string) {
 		header["Content-Type"] = value
 	}
 }
+
+func writeContentLength(w http.ResponseWriter, value int) {
+	w.Header().Set("Content-Length", strconv.Itoa(value))
+}
diff --git a/render/render_test.go b/render/render_test.go
index c9db635f..4ab94cbc 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -39,6 +39,8 @@ func TestRenderJSON(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "{\"foo\":\"bar\",\"html\":\"\\u003cb\\u003e\"}", w.Body.String())
 	assert.Equal(t, "application/json; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "36", w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderJSONError(t *testing.T) {
@@ -61,6 +63,8 @@ func TestRenderIndentedJSON(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "{\n    \"bar\": \"foo\",\n    \"foo\": \"bar\"\n}", w.Body.String())
 	assert.Equal(t, "application/json; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "38", w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderIndentedJSONPanics(t *testing.T) {
@@ -86,6 +90,7 @@ func TestRenderSecureJSON(t *testing.T) {
 	assert.NoError(t, err1)
 	assert.Equal(t, "{\"foo\":\"bar\"}", w1.Body.String())
 	assert.Equal(t, "application/json; charset=utf-8", w1.Header().Get("Content-Type"))
+	assert.Equal(t, "13", w1.Header().Get("Content-Length"))
 
 	w2 := httptest.NewRecorder()
 	datas := []map[string]any{{
@@ -98,6 +103,7 @@ func TestRenderSecureJSON(t *testing.T) {
 	assert.NoError(t, err2)
 	assert.Equal(t, "while(1);[{\"foo\":\"bar\"},{\"bar\":\"foo\"}]", w2.Body.String())
 	assert.Equal(t, "application/json; charset=utf-8", w2.Header().Get("Content-Type"))
+	assert.Equal(t, "38", w2.Header().Get("Content-Length"))
 }
 
 func TestRenderSecureJSONFail(t *testing.T) {
@@ -123,6 +129,7 @@ func TestRenderJsonpJSON(t *testing.T) {
 	assert.NoError(t, err1)
 	assert.Equal(t, "x({\"foo\":\"bar\"});", w1.Body.String())
 	assert.Equal(t, "application/javascript; charset=utf-8", w1.Header().Get("Content-Type"))
+	assert.Equal(t, "17", w1.Header().Get("Content-Length"))
 
 	w2 := httptest.NewRecorder()
 	datas := []map[string]any{{
@@ -135,6 +142,8 @@ func TestRenderJsonpJSON(t *testing.T) {
 	assert.NoError(t, err2)
 	assert.Equal(t, "x([{\"foo\":\"bar\"},{\"bar\":\"foo\"}]);", w2.Body.String())
 	assert.Equal(t, "application/javascript; charset=utf-8", w2.Header().Get("Content-Type"))
+	assert.Equal(t, "33", w2.Header().Get("Content-Length"))
+
 }
 
 type errorWriter struct {
@@ -195,6 +204,7 @@ func TestRenderJsonpJSONError2(t *testing.T) {
 
 	assert.Equal(t, "{\"foo\":\"bar\"}", w.Body.String())
 	assert.Equal(t, "application/javascript; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "13", w.Header().Get("Content-Length"))
 }
 
 func TestRenderJsonpJSONFail(t *testing.T) {
@@ -218,6 +228,7 @@ func TestRenderAsciiJSON(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "{\"lang\":\"GO\\u8bed\\u8a00\",\"tag\":\"\\u003cbr\\u003e\"}", w1.Body.String())
 	assert.Equal(t, "application/json", w1.Header().Get("Content-Type"))
+	assert.Equal(t, "48", w1.Header().Get("Content-Length"))
 
 	w2 := httptest.NewRecorder()
 	data2 := 3.1415926
@@ -225,6 +236,8 @@ func TestRenderAsciiJSON(t *testing.T) {
 	err = (AsciiJSON{data2}).Render(w2)
 	assert.NoError(t, err)
 	assert.Equal(t, "3.1415926", w2.Body.String())
+	assert.Equal(t, "9", w2.Header().Get("Content-Length"))
+
 }
 
 func TestRenderAsciiJSONFail(t *testing.T) {
@@ -286,6 +299,8 @@ b:
 	assert.NoError(t, err)
 	assert.Equal(t, "|4-\n    a : Easy!\n    b:\n    \tc: 2\n    \td: [3, 4]\n    \t\n", w.Body.String())
 	assert.Equal(t, "application/x-yaml; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "56", w.Header().Get("Content-Length"))
+
 }
 
 type fail struct{}
@@ -314,6 +329,8 @@ func TestRenderTOML(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "foo = 'bar'\nhtml = '<b>'\n", w.Body.String())
 	assert.Equal(t, "application/toml; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "25", w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderTOMLFail(t *testing.T) {
@@ -342,6 +359,8 @@ func TestRenderProtoBuf(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, string(protoData), w.Body.String())
 	assert.Equal(t, "application/x-protobuf", w.Header().Get("Content-Type"))
+	assert.Equal(t, strconv.Itoa(len(string(protoData))), w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderProtoBufFail(t *testing.T) {
@@ -419,6 +438,8 @@ func TestRenderData(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "#!PNG some raw data", w.Body.String())
 	assert.Equal(t, "image/png", w.Header().Get("Content-Type"))
+	assert.Equal(t, "19", w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderString(t *testing.T) {
@@ -451,6 +472,8 @@ func TestRenderStringLenZero(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "hola %s %d", w.Body.String())
 	assert.Equal(t, "text/plain; charset=utf-8", w.Header().Get("Content-Type"))
+	assert.Equal(t, "10", w.Header().Get("Content-Length"))
+
 }
 
 func TestRenderHTMLTemplate(t *testing.T) {
diff --git a/render/text.go b/render/text.go
index 77eafdfd..24a7c125 100644
--- a/render/text.go
+++ b/render/text.go
@@ -36,6 +36,12 @@ func WriteString(w http.ResponseWriter, format string, data []any) (err error) {
 		_, err = fmt.Fprintf(w, format, data...)
 		return
 	}
-	_, err = w.Write(bytesconv.StringToBytes(format))
+
+	bytes := bytesconv.StringToBytes(format)
+
+	writeContentLength(w, len(bytes))
+
+	_, err = w.Write(bytes)
+
 	return
 }
diff --git a/render/toml.go b/render/toml.go
index 40f044c8..2cd1f212 100644
--- a/render/toml.go
+++ b/render/toml.go
@@ -26,6 +26,8 @@ func (r TOML) Render(w http.ResponseWriter) error {
 		return err
 	}
 
+	writeContentLength(w, len(bytes))
+
 	_, err = w.Write(bytes)
 	return err
 }
diff --git a/render/yaml.go b/render/yaml.go
index fc927c1f..fbc1e623 100644
--- a/render/yaml.go
+++ b/render/yaml.go
@@ -26,6 +26,8 @@ func (r YAML) Render(w http.ResponseWriter) error {
 		return err
 	}
 
+	writeContentLength(w, len(bytes))
+
 	_, err = w.Write(bytes)
 	return err
 }