diff --git a/blobs.go b/blobs.go
index c606d914..b0c89d1f 100644
--- a/blobs.go
+++ b/blobs.go
@@ -49,8 +49,8 @@ type Descriptor struct {
 	// encoded as utf-8.
 	MediaType string `json:"mediaType,omitempty"`
 
-	// Length in bytes of content.
-	Length int64 `json:"length,omitempty"`
+	// Size in bytes of content.
+	Size int64 `json:"size,omitempty"`
 
 	// Digest uniquely identifies the content. A byte stream can be verified
 	// against against this digest.
diff --git a/docs/notifications.md b/docs/notifications.md
index 09f41d8e..4875cf17 100644
--- a/docs/notifications.md
+++ b/docs/notifications.md
@@ -84,8 +84,9 @@ manifest:
    "action": "push",
    "target": {
       "mediaType": "application/vnd.docker.distribution.manifest.v1+json",
-      "length": 1,
+      "size": 1,
       "digest": "sha256:0123456789abcdef0",
+      "length": 1,
       "repository": "library/test",
       "url": "http://example.com/v2/library/test/manifests/latest"
    },
@@ -105,6 +106,11 @@ manifest:
 }
 ```
 
+> __NOTE(stevvooe):__ As of version 2.1, the `length` field for event targets
+> is being deprecated for the `size` field, bringing the target in line with
+> common nomenclature. Both will continue to be set for the foreseeable
+> future. Newer code should favor `size` but accept either.
+
 ## Envelope
 
 The envelope contains one or more events, with the following json structure:
diff --git a/notifications/bridge.go b/notifications/bridge.go
index fff45a4f..b97925a5 100644
--- a/notifications/bridge.go
+++ b/notifications/bridge.go
@@ -97,6 +97,7 @@ func (b *bridge) createManifestEvent(action string, repo string, sm *manifest.Si
 	}
 
 	event.Target.Length = int64(len(p))
+	event.Target.Size = int64(len(p))
 	event.Target.Digest, err = digest.FromBytes(p)
 	if err != nil {
 		return nil, err
@@ -122,6 +123,7 @@ func (b *bridge) createBlobEventAndWrite(action string, repo string, desc distri
 func (b *bridge) createBlobEvent(action string, repo string, desc distribution.Descriptor) (*Event, error) {
 	event := b.createEvent(action)
 	event.Target.Descriptor = desc
+	event.Target.Length = desc.Size
 	event.Target.Repository = repo
 
 	var err error
diff --git a/notifications/event.go b/notifications/event.go
index a898021b..97030026 100644
--- a/notifications/event.go
+++ b/notifications/event.go
@@ -54,6 +54,10 @@ type Event struct {
 
 		distribution.Descriptor
 
+		// Length in bytes of content. Same as Size field in Descriptor.
+		// Provided for backwards compatibility.
+		Length int64 `json:"length,omitempty"`
+
 		// Repository identifies the named repository.
 		Repository string `json:"repository,omitempty"`
 
diff --git a/notifications/event_test.go b/notifications/event_test.go
index c413ce79..ac4dfd93 100644
--- a/notifications/event_test.go
+++ b/notifications/event_test.go
@@ -22,8 +22,9 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
          "action": "push",
          "target": {
             "mediaType": "application/vnd.docker.distribution.manifest.v1+json",
-            "length": 1,
+            "size": 1,
             "digest": "sha256:0123456789abcdef0",
+            "length": 1,
             "repository": "library/test",
             "url": "http://example.com/v2/library/test/manifests/latest"
          },
@@ -47,8 +48,9 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
          "action": "push",
          "target": {
             "mediaType": "application/vnd.docker.container.image.rootfs.diff+x-gtar",
-            "length": 2,
+            "size": 2,
             "digest": "tarsum.v2+sha256:0123456789abcdef1",
+            "length": 2,
             "repository": "library/test",
             "url": "http://example.com/v2/library/test/manifests/latest"
          },
@@ -72,8 +74,9 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
          "action": "push",
          "target": {
             "mediaType": "application/vnd.docker.container.image.rootfs.diff+x-gtar",
-            "length": 3,
+            "size": 3,
             "digest": "tarsum.v2+sha256:0123456789abcdef2",
+            "length": 3,
             "repository": "library/test",
             "url": "http://example.com/v2/library/test/manifests/latest"
          },
@@ -115,7 +118,8 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
 	manifestPush = prototype
 	manifestPush.ID = "asdf-asdf-asdf-asdf-0"
 	manifestPush.Target.Digest = "sha256:0123456789abcdef0"
-	manifestPush.Target.Length = int64(1)
+	manifestPush.Target.Length = 1
+	manifestPush.Target.Size = 1
 	manifestPush.Target.MediaType = manifest.ManifestMediaType
 	manifestPush.Target.Repository = "library/test"
 	manifestPush.Target.URL = "http://example.com/v2/library/test/manifests/latest"
@@ -125,6 +129,7 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
 	layerPush0.ID = "asdf-asdf-asdf-asdf-1"
 	layerPush0.Target.Digest = "tarsum.v2+sha256:0123456789abcdef1"
 	layerPush0.Target.Length = 2
+	layerPush0.Target.Size = 2
 	layerPush0.Target.MediaType = layerMediaType
 	layerPush0.Target.Repository = "library/test"
 	layerPush0.Target.URL = "http://example.com/v2/library/test/manifests/latest"
@@ -134,6 +139,7 @@ func TestEventEnvelopeJSONFormat(t *testing.T) {
 	layerPush1.ID = "asdf-asdf-asdf-asdf-2"
 	layerPush1.Target.Digest = "tarsum.v2+sha256:0123456789abcdef2"
 	layerPush1.Target.Length = 3
+	layerPush1.Target.Size = 3
 	layerPush1.Target.MediaType = layerMediaType
 	layerPush1.Target.Repository = "library/test"
 	layerPush1.Target.URL = "http://example.com/v2/library/test/manifests/latest"
diff --git a/registry/client/repository.go b/registry/client/repository.go
index 840a7af6..fc90cb6e 100644
--- a/registry/client/repository.go
+++ b/registry/client/repository.go
@@ -343,7 +343,7 @@ func (bs *blobs) Open(ctx context.Context, dgst digest.Digest) (distribution.Rea
 		return nil, err
 	}
 
-	return transport.NewHTTPReadSeeker(bs.client, blobURL, stat.Length), nil
+	return transport.NewHTTPReadSeeker(bs.client, blobURL, stat.Size), nil
 }
 
 func (bs *blobs) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
@@ -366,7 +366,7 @@ func (bs *blobs) Put(ctx context.Context, mediaType string, p []byte) (distribut
 
 	desc := distribution.Descriptor{
 		MediaType: mediaType,
-		Length:    int64(len(p)),
+		Size:      int64(len(p)),
 		Digest:    dgstr.Digest(),
 	}
 
@@ -435,7 +435,7 @@ func (bs *blobStatter) Stat(ctx context.Context, dgst digest.Digest) (distributi
 
 		return distribution.Descriptor{
 			MediaType: resp.Header.Get("Content-Type"),
-			Length:    length,
+			Size:      length,
 			Digest:    dgst,
 		}, nil
 	case http.StatusNotFound:
diff --git a/registry/client/repository_test.go b/registry/client/repository_test.go
index 642ef998..3a91be98 100644
--- a/registry/client/repository_test.go
+++ b/registry/client/repository_test.go
@@ -127,8 +127,8 @@ func TestBlobExists(t *testing.T) {
 		t.Fatalf("Unexpected digest: %s, expected %s", stat.Digest, d1)
 	}
 
-	if stat.Length != int64(len(b1)) {
-		t.Fatalf("Unexpected length: %d, expected %d", stat.Length, len(b1))
+	if stat.Size != int64(len(b1)) {
+		t.Fatalf("Unexpected length: %d, expected %d", stat.Size, len(b1))
 	}
 
 	// TODO(dmcgowan): Test error cases and ErrBlobUnknown case
@@ -244,14 +244,14 @@ func TestBlobUploadChunked(t *testing.T) {
 
 	blob, err := upload.Commit(ctx, distribution.Descriptor{
 		Digest: dgst,
-		Length: int64(len(b1)),
+		Size:   int64(len(b1)),
 	})
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if blob.Length != int64(len(b1)) {
-		t.Fatalf("Unexpected blob size: %d; expected: %d", blob.Length, len(b1))
+	if blob.Size != int64(len(b1)) {
+		t.Fatalf("Unexpected blob size: %d; expected: %d", blob.Size, len(b1))
 	}
 }
 
@@ -352,14 +352,14 @@ func TestBlobUploadMonolithic(t *testing.T) {
 
 	blob, err := upload.Commit(ctx, distribution.Descriptor{
 		Digest: dgst,
-		Length: int64(len(b1)),
+		Size:   int64(len(b1)),
 	})
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if blob.Length != int64(len(b1)) {
-		t.Fatalf("Unexpected blob size: %d; expected: %d", blob.Length, len(b1))
+	if blob.Size != int64(len(b1)) {
+		t.Fatalf("Unexpected blob size: %d; expected: %d", blob.Size, len(b1))
 	}
 }
 
diff --git a/registry/storage/blob_test.go b/registry/storage/blob_test.go
index 569f756d..0dbfe810 100644
--- a/registry/storage/blob_test.go
+++ b/registry/storage/blob_test.go
@@ -178,7 +178,7 @@ func TestSimpleBlobRead(t *testing.T) {
 		t.Fatalf("error getting seeker size for random layer: %v", err)
 	}
 
-	descBefore := distribution.Descriptor{Digest: dgst, MediaType: "application/octet-stream", Length: randomLayerSize}
+	descBefore := distribution.Descriptor{Digest: dgst, MediaType: "application/octet-stream", Size: randomLayerSize}
 	t.Logf("desc: %v", descBefore)
 
 	desc, err = addBlob(ctx, bs, descBefore, randomLayerReader)
@@ -186,8 +186,8 @@ func TestSimpleBlobRead(t *testing.T) {
 		t.Fatalf("error adding blob to blobservice: %v", err)
 	}
 
-	if desc.Length != randomLayerSize {
-		t.Fatalf("committed blob has incorrect length: %v != %v", desc.Length, randomLayerSize)
+	if desc.Size != randomLayerSize {
+		t.Fatalf("committed blob has incorrect length: %v != %v", desc.Size, randomLayerSize)
 	}
 
 	rc, err = bs.Open(ctx, desc.Digest) // note that we are opening with original digest.
@@ -330,8 +330,8 @@ func addBlob(ctx context.Context, bs distribution.BlobIngester, desc distributio
 
 	if nn, err := io.Copy(wr, rd); err != nil {
 		return distribution.Descriptor{}, err
-	} else if nn != desc.Length {
-		return distribution.Descriptor{}, fmt.Errorf("incorrect number of bytes copied: %v != %v", nn, desc.Length)
+	} else if nn != desc.Size {
+		return distribution.Descriptor{}, fmt.Errorf("incorrect number of bytes copied: %v != %v", nn, desc.Size)
 	}
 
 	return wr.Commit(ctx, desc)
diff --git a/registry/storage/blobserver.go b/registry/storage/blobserver.go
index a7b42681..d0b3204c 100644
--- a/registry/storage/blobserver.go
+++ b/registry/storage/blobserver.go
@@ -41,7 +41,7 @@ func (bs *blobServer) ServeBlob(ctx context.Context, w http.ResponseWriter, r *h
 		http.Redirect(w, r, redirectURL, http.StatusTemporaryRedirect)
 	case driver.ErrUnsupportedMethod:
 		// Fallback to serving the content directly.
-		br, err := newFileReader(ctx, bs.driver, path, desc.Length)
+		br, err := newFileReader(ctx, bs.driver, path, desc.Size)
 		if err != nil {
 			return err
 		}
@@ -61,7 +61,7 @@ func (bs *blobServer) ServeBlob(ctx context.Context, w http.ResponseWriter, r *h
 
 		if w.Header().Get("Content-Length") == "" {
 			// Set the content length if not already set.
-			w.Header().Set("Content-Length", fmt.Sprint(desc.Length))
+			w.Header().Set("Content-Length", fmt.Sprint(desc.Size))
 		}
 
 		http.ServeContent(w, r, desc.Digest.String(), time.Time{}, br)
diff --git a/registry/storage/blobstore.go b/registry/storage/blobstore.go
index afe42847..484e2106 100644
--- a/registry/storage/blobstore.go
+++ b/registry/storage/blobstore.go
@@ -50,7 +50,7 @@ func (bs *blobStore) Open(ctx context.Context, dgst digest.Digest) (distribution
 		return nil, err
 	}
 
-	return newFileReader(ctx, bs.driver, path, desc.Length)
+	return newFileReader(ctx, bs.driver, path, desc.Size)
 }
 
 // Put stores the content p in the blob store, calculating the digest. If the
@@ -81,7 +81,7 @@ func (bs *blobStore) Put(ctx context.Context, mediaType string, p []byte) (distr
 	// TODO(stevvooe): Write out mediatype here, as well.
 
 	return distribution.Descriptor{
-		Length: int64(len(p)),
+		Size: int64(len(p)),
 
 		// NOTE(stevvooe): The central blob store firewalls media types from
 		// other users. The caller should look this up and override the value
@@ -179,7 +179,7 @@ func (bs *blobStatter) Stat(ctx context.Context, dgst digest.Digest) (distributi
 	// mediatype that overrides the main one.
 
 	return distribution.Descriptor{
-		Length: fi.Size(),
+		Size: fi.Size(),
 
 		// NOTE(stevvooe): The central blob store firewalls media types from
 		// other users. The caller should look this up and override the value
diff --git a/registry/storage/blobwriter.go b/registry/storage/blobwriter.go
index 4189d517..b39c851e 100644
--- a/registry/storage/blobwriter.go
+++ b/registry/storage/blobwriter.go
@@ -148,7 +148,7 @@ func (bw *blobWriter) validateBlob(ctx context.Context, desc distribution.Descri
 			// NOTE(stevvooe): We really don't care if the file is
 			// not actually present for the reader. We now assume
 			// that the desc length is zero.
-			desc.Length = 0
+			desc.Size = 0
 		default:
 			// Any other error we want propagated up the stack.
 			return distribution.Descriptor{}, err
@@ -161,14 +161,14 @@ func (bw *blobWriter) validateBlob(ctx context.Context, desc distribution.Descri
 		bw.size = fi.Size()
 	}
 
-	if desc.Length > 0 {
-		if desc.Length != bw.size {
+	if desc.Size > 0 {
+		if desc.Size != bw.size {
 			return distribution.Descriptor{}, distribution.ErrBlobInvalidLength
 		}
 	} else {
 		// if provided 0 or negative length, we can assume caller doesn't know or
 		// care about length.
-		desc.Length = bw.size
+		desc.Size = bw.size
 	}
 
 	// TODO(stevvooe): This section is very meandering. Need to be broken down
@@ -216,7 +216,7 @@ func (bw *blobWriter) validateBlob(ctx context.Context, desc distribution.Descri
 			}
 
 			// Read the file from the backend driver and validate it.
-			fr, err := newFileReader(ctx, bw.bufferedFileWriter.driver, bw.path, desc.Length)
+			fr, err := newFileReader(ctx, bw.bufferedFileWriter.driver, bw.path, desc.Size)
 			if err != nil {
 				return distribution.Descriptor{}, err
 			}
diff --git a/registry/storage/cache/cache.go b/registry/storage/cache/cache.go
index 79e6d9c8..10a39091 100644
--- a/registry/storage/cache/cache.go
+++ b/registry/storage/cache/cache.go
@@ -23,8 +23,8 @@ func ValidateDescriptor(desc distribution.Descriptor) error {
 		return err
 	}
 
-	if desc.Length < 0 {
-		return fmt.Errorf("cache: invalid length in descriptor: %v < 0", desc.Length)
+	if desc.Size < 0 {
+		return fmt.Errorf("cache: invalid length in descriptor: %v < 0", desc.Size)
 	}
 
 	if desc.MediaType == "" {
diff --git a/registry/storage/cache/redis/redis.go b/registry/storage/cache/redis/redis.go
index 29bbe3bc..64010a09 100644
--- a/registry/storage/cache/redis/redis.go
+++ b/registry/storage/cache/redis/redis.go
@@ -66,17 +66,20 @@ func (rbds *redisBlobDescriptorService) Stat(ctx context.Context, dgst digest.Di
 // stat provides an internal stat call that takes a connection parameter. This
 // allows some internal management of the connection scope.
 func (rbds *redisBlobDescriptorService) stat(ctx context.Context, conn redis.Conn, dgst digest.Digest) (distribution.Descriptor, error) {
-	reply, err := redis.Values(conn.Do("HMGET", rbds.blobDescriptorHashKey(dgst), "digest", "length", "mediatype"))
+	reply, err := redis.Values(conn.Do("HMGET", rbds.blobDescriptorHashKey(dgst), "digest", "size", "mediatype"))
 	if err != nil {
 		return distribution.Descriptor{}, err
 	}
 
-	if len(reply) < 2 || reply[0] == nil || reply[1] == nil { // don't care if mediatype is nil
+	// NOTE(stevvooe): The "size" field used to be "length". We treat a
+	// missing "size" field here as an unknown blob, which causes a cache
+	// miss, effectively migrating the field.
+	if len(reply) < 3 || reply[0] == nil || reply[1] == nil { // don't care if mediatype is nil
 		return distribution.Descriptor{}, distribution.ErrBlobUnknown
 	}
 
 	var desc distribution.Descriptor
-	if _, err := redis.Scan(reply, &desc.Digest, &desc.Length, &desc.MediaType); err != nil {
+	if _, err := redis.Scan(reply, &desc.Digest, &desc.Size, &desc.MediaType); err != nil {
 		return distribution.Descriptor{}, err
 	}
 
@@ -104,7 +107,7 @@ func (rbds *redisBlobDescriptorService) SetDescriptor(ctx context.Context, dgst
 func (rbds *redisBlobDescriptorService) setDescriptor(ctx context.Context, conn redis.Conn, dgst digest.Digest, desc distribution.Descriptor) error {
 	if _, err := conn.Do("HMSET", rbds.blobDescriptorHashKey(dgst),
 		"digest", desc.Digest,
-		"length", desc.Length); err != nil {
+		"size", desc.Size); err != nil {
 		return err
 	}
 
diff --git a/registry/storage/cache/suite.go b/registry/storage/cache/suite.go
index ceefab97..f74d9f9e 100644
--- a/registry/storage/cache/suite.go
+++ b/registry/storage/cache/suite.go
@@ -35,14 +35,14 @@ func checkBlobDescriptorCacheEmptyRepository(t *testing.T, ctx context.Context,
 
 	if err := cache.SetDescriptor(ctx, "", distribution.Descriptor{
 		Digest:    "sha384:abc",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}); err != digest.ErrDigestInvalidFormat {
 		t.Fatalf("expected error with invalid digest: %v", err)
 	}
 
 	if err := cache.SetDescriptor(ctx, "sha384:abc", distribution.Descriptor{
 		Digest:    "",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}); err == nil {
 		t.Fatalf("expected error setting value on invalid descriptor")
 	}
@@ -60,7 +60,7 @@ func checkBlobDescriptorCacheSetAndRead(t *testing.T, ctx context.Context, provi
 	localDigest := digest.Digest("sha384:abc")
 	expected := distribution.Descriptor{
 		Digest:    "sha256:abc",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}
 
 	cache, err := provider.RepositoryScoped("foo/bar")