diff --git a/pkg/cmd/api/api.go b/pkg/cmd/api/api.go
index b828c607c..b4a8dbdff 100644
--- a/pkg/cmd/api/api.go
+++ b/pkg/cmd/api/api.go
@@ -103,13 +103,16 @@ func apiRun(opts *ApiOptions) error {
 	}
 
 	if opts.RequestInputFile != "" {
-		file, err := openUserFile(opts.RequestInputFile, opts.IO.In)
+		file, size, err := openUserFile(opts.RequestInputFile, opts.IO.In)
 		if err != nil {
 			return err
 		}
 		defer file.Close()
 		requestPath = addQuery(requestPath, params)
 		requestBody = file
+		if size >= 0 {
+			requestHeaders = append([]string{fmt.Sprintf("Content-Length: %d", size)}, requestHeaders...)
+		}
 	}
 
 	httpClient, err := opts.HttpClient()
@@ -240,19 +243,36 @@ func magicFieldValue(v string, stdin io.ReadCloser) (interface{}, error) {
 }
 
 func readUserFile(fn string, stdin io.ReadCloser) ([]byte, error) {
-	r, err := openUserFile(fn, stdin)
-	if err != nil {
-		return nil, err
+	var r io.ReadCloser
+	if fn == "-" {
+		r = stdin
+	} else {
+		var err error
+		r, err = os.Open(fn)
+		if err != nil {
+			return nil, err
+		}
 	}
 	defer r.Close()
 	return ioutil.ReadAll(r)
 }
 
-func openUserFile(fn string, stdin io.ReadCloser) (io.ReadCloser, error) {
+func openUserFile(fn string, stdin io.ReadCloser) (io.ReadCloser, int64, error) {
 	if fn == "-" {
-		return stdin, nil
+		return stdin, -1, nil
 	}
-	return os.Open(fn)
+
+	r, err := os.Open(fn)
+	if err != nil {
+		return r, -1, err
+	}
+
+	s, err := os.Stat(fn)
+	if err != nil {
+		return r, -1, err
+	}
+
+	return r, s.Size(), nil
 }
 
 func parseErrorResponse(r io.Reader, statusCode int) (io.Reader, string, error) {
diff --git a/pkg/cmd/api/api_test.go b/pkg/cmd/api/api_test.go
index c121455db..100c1257e 100644
--- a/pkg/cmd/api/api_test.go
+++ b/pkg/cmd/api/api_test.go
@@ -247,41 +247,78 @@ func Test_apiRun(t *testing.T) {
 }
 
 func Test_apiRun_inputFile(t *testing.T) {
-	io, stdin, _, _ := iostreams.Test()
-	resp := &http.Response{StatusCode: 204}
+	tests := []struct {
+		name          string
+		inputFile     string
+		inputContents []byte
 
-	options := ApiOptions{
-		RequestPath:      "hello",
-		RequestInputFile: "-",
-		RawFields:        []string{"a=b", "c=d"},
-
-		IO: io,
-		HttpClient: func() (*http.Client, error) {
-			var tr roundTripper = func(req *http.Request) (*http.Response, error) {
-				resp.Request = req
-				return resp, nil
-			}
-			return &http.Client{Transport: tr}, nil
+		contentLength    int64
+		expectedContents []byte
+	}{
+		{
+			name:          "stdin",
+			inputFile:     "-",
+			inputContents: []byte("I WORK OUT"),
+			contentLength: 0,
+		},
+		{
+			name:          "from file",
+			inputFile:     "gh-test-file",
+			inputContents: []byte("I WORK OUT"),
+			contentLength: 10,
 		},
 	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			io, stdin, _, _ := iostreams.Test()
+			resp := &http.Response{StatusCode: 204}
 
-	fmt.Fprintln(stdin, "I WORK OUT")
+			inputFile := tt.inputFile
+			if tt.inputFile == "-" {
+				_, _ = stdin.Write(tt.inputContents)
+			} else {
+				f, err := ioutil.TempFile("", tt.inputFile)
+				if err != nil {
+					t.Fatal(err)
+				}
+				_, _ = f.Write(tt.inputContents)
+				f.Close()
+				t.Cleanup(func() { os.Remove(f.Name()) })
+				inputFile = f.Name()
+			}
 
-	err := apiRun(&options)
-	if err != nil {
-		t.Errorf("got error %v", err)
+			var bodyBytes []byte
+			options := ApiOptions{
+				RequestPath:      "hello",
+				RequestInputFile: inputFile,
+				RawFields:        []string{"a=b", "c=d"},
+
+				IO: io,
+				HttpClient: func() (*http.Client, error) {
+					var tr roundTripper = func(req *http.Request) (*http.Response, error) {
+						var err error
+						if bodyBytes, err = ioutil.ReadAll(req.Body); err != nil {
+							return nil, err
+						}
+						resp.Request = req
+						return resp, nil
+					}
+					return &http.Client{Transport: tr}, nil
+				},
+			}
+
+			err := apiRun(&options)
+			if err != nil {
+				t.Errorf("got error %v", err)
+			}
+
+			assert.Equal(t, "POST", resp.Request.Method)
+			assert.Equal(t, "/hello?a=b&c=d", resp.Request.URL.RequestURI())
+			assert.Equal(t, tt.contentLength, resp.Request.ContentLength)
+			assert.Equal(t, "", resp.Request.Header.Get("Content-Type"))
+			assert.Equal(t, tt.inputContents, bodyBytes)
+		})
 	}
-
-	assert.Equal(t, "POST", resp.Request.Method)
-	assert.Equal(t, "/hello?a=b&c=d", resp.Request.URL.RequestURI())
-	assert.Equal(t, "", resp.Request.Header.Get("Content-Length"))
-	assert.Equal(t, "", resp.Request.Header.Get("Content-Type"))
-
-	bb, err := ioutil.ReadAll(resp.Request.Body)
-	if err != nil {
-		t.Errorf("got error %v", err)
-	}
-	assert.Equal(t, "I WORK OUT\n", string(bb))
 }
 
 func Test_parseFields(t *testing.T) {
@@ -400,7 +437,7 @@ func Test_openUserFile(t *testing.T) {
 	f.Close()
 	t.Cleanup(func() { os.Remove(f.Name()) })
 
-	file, err := openUserFile(f.Name(), nil)
+	file, length, err := openUserFile(f.Name(), nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -411,5 +448,6 @@ func Test_openUserFile(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	assert.Equal(t, int64(13), length)
 	assert.Equal(t, "file contents", string(fb))
 }
diff --git a/pkg/cmd/api/http.go b/pkg/cmd/api/http.go
index 4db21b286..e393bb593 100644
--- a/pkg/cmd/api/http.go
+++ b/pkg/cmd/api/http.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"strconv"
 	"strings"
 )
 
@@ -62,7 +63,16 @@ func httpRequest(client *http.Client, method string, p string, params interface{
 		if idx == -1 {
 			return nil, fmt.Errorf("header %q requires a value separated by ':'", h)
 		}
-		req.Header.Add(h[0:idx], strings.TrimSpace(h[idx+1:]))
+		name, value := h[0:idx], strings.TrimSpace(h[idx+1:])
+		if strings.EqualFold(name, "Content-Length") {
+			length, err := strconv.ParseInt(value, 10, 0)
+			if err != nil {
+				return nil, err
+			}
+			req.ContentLength = length
+		} else {
+			req.Header.Add(name, value)
+		}
 	}
 	if bodyIsJSON && req.Header.Get("Content-Type") == "" {
 		req.Header.Set("Content-Type", "application/json; charset=utf-8")