diff --git a/dom/canvas/ImageBitmap.cpp b/dom/canvas/ImageBitmap.cpp
index f0c55a23fedc..74a7bae447f0 100644
--- a/dom/canvas/ImageBitmap.cpp
+++ b/dom/canvas/ImageBitmap.cpp
@@ -1549,21 +1549,6 @@ ImageBitmap::FindOptimalFormat(const Optional<Sequence<ImageBitmapFormat>>& aPos
   }
 }
 
-int32_t
-ImageBitmap::MappedDataLength(ImageBitmapFormat aFormat, ErrorResult& aRv)
-{
-  if (!mDataWrapper) {
-    aRv.Throw(NS_ERROR_NOT_AVAILABLE);
-    return 0;
-  }
-
-  if (aFormat == mDataWrapper->GetFormat()) {
-    return mDataWrapper->GetBufferLength();
-  } else {
-    return CalculateImageBufferSize(aFormat, Width(), Height());
-  }
-}
-
 size_t
 ImageBitmap::GetAllocatedSize() const
 {
diff --git a/dom/canvas/ImageBitmap.h b/dom/canvas/ImageBitmap.h
index e5ea0d3b7341..389fb10fa7d1 100644
--- a/dom/canvas/ImageBitmap.h
+++ b/dom/canvas/ImageBitmap.h
@@ -153,9 +153,6 @@ public:
   FindOptimalFormat(const Optional<Sequence<ImageBitmapFormat>>& aPossibleFormats,
                     ErrorResult& aRv);
 
-  int32_t
-  MappedDataLength(ImageBitmapFormat aFormat, ErrorResult& aRv);
-
   size_t GetAllocatedSize() const;
 
   void OnShutdown();
diff --git a/dom/canvas/ImageBitmapUtils.cpp b/dom/canvas/ImageBitmapUtils.cpp
index 28e76bedc30b..9c827382e32e 100644
--- a/dom/canvas/ImageBitmapUtils.cpp
+++ b/dom/canvas/ImageBitmapUtils.cpp
@@ -2730,16 +2730,6 @@ GetChannelCountOfImageFormat(ImageBitmapFormat aFormat)
   return format->GetChannelCount();
 }
 
-uint32_t
-CalculateImageBufferSize(ImageBitmapFormat aFormat,
-                         uint32_t aWidth, uint32_t aHeight)
-{
-  UtilsUniquePtr format = Utils::GetUtils(aFormat);
-  MOZ_ASSERT(format, "Cannot get a valid ImageBitmapFormatUtils instance.");
-
-  return format->NeededBufferSize(aWidth, aHeight);
-}
-
 UniquePtr<ImagePixelLayout>
 CopyAndConvertImageData(ImageBitmapFormat aSrcFormat,
                         const uint8_t* aSrcBuffer,
diff --git a/dom/canvas/ImageBitmapUtils.h b/dom/canvas/ImageBitmapUtils.h
index 39be43d8ae54..9e86fadf6af2 100644
--- a/dom/canvas/ImageBitmapUtils.h
+++ b/dom/canvas/ImageBitmapUtils.h
@@ -48,14 +48,6 @@ CreatePixelLayoutFromPlanarYCbCrData(const layers::PlanarYCbCrData* aData);
 uint8_t
 GetChannelCountOfImageFormat(ImageBitmapFormat aFormat);
 
-/*
- * Get the needed buffer size to store the image data in the given
- * ImageBitmapFormat with the given width and height.
- */
-uint32_t
-CalculateImageBufferSize(ImageBitmapFormat aFormat,
-                         uint32_t aWidth, uint32_t aHeight);
-
 /*
  * This function always copies the image data in _aSrcBuffer_ into _aDstBuffer_
  * and it also performs color conversion if the _aSrcFormat_ and the
diff --git a/dom/webidl/ImageBitmap.webidl b/dom/webidl/ImageBitmap.webidl
index 5d91a64686b1..edc07c2a50d5 100644
--- a/dom/webidl/ImageBitmap.webidl
+++ b/dom/webidl/ImageBitmap.webidl
@@ -397,6 +397,4 @@ typedef sequence<ChannelPixelLayout> ImagePixelLayout;
 partial interface ImageBitmap {
     [Throws, Func="mozilla::dom::DOMPrefs::canvas_imagebitmap_extensions_enabled"]
     ImageBitmapFormat               findOptimalFormat (optional sequence<ImageBitmapFormat> aPossibleFormats);
-    [Throws, Func="mozilla::dom::DOMPrefs::canvas_imagebitmap_extensions_enabled"]
-    long                            mappedDataLength (ImageBitmapFormat aFormat);
 };