Elements Image Size Dialog Box "Pixel Dimensions"

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Before you dismiss this question, look at your Image>Resize>Image Size dialog box. 
What does "Pixel Dimensions" there mean? 
It is identified with an amount preceding an "M" but it's hard to know what it refers to. 
If I multiply dimensions - pixel width by length - for resolution/megapixels, it does not match the M amount. 
When I look at the file size/megabytes for the image, it doesn't match the M amount. 
So what does the M mean?
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Kathleen Madeline

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Posted 2 years ago

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Michel BRETECHER, Champion

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Kathy,
The 'M' refers to the size of the document in bytes; pixel width by length by channel (R,G,B).
You can show this 'M' document size in the left of the bottom bar of your document window. There is a > on the right of the shown property to change the property which is displayed on that bar.
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Kathleen Madeline

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What you said made me investigate further. 
The RGB info is figured into it, for sure, as seen in my snips I'm including. 
I hovered the cursor for more info and found it was a measure of size in pixels, not bytes. 
The channels are figured into it by how many channels are involved.
RGB: W x L X 3 = pixel dimensions.  Grayscale: W x L x 1 = pixel dimensions. 
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Michel BRETECHER, Champion

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See:
http://www.dictionary.com/browse/pixel
A pixel refers to the site, which has three properties.
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Kathleen Madeline

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You do agree, though, that the M actually means megapixels and not megabytes?
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Michel BRETECHER, Champion

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You do agree, though, that the M actually means megapixels and not megabytes?
It's only megabytes if you are in 8-bits depth color (would be double that count in 16-bits)  but it's not megapixels either. Read the definition of pixels: you have always the same pixels (photo sites) whether it's in RGB or grayscale, 8 or 16-bits.
I'll leave others give the correct name of the M unit, but anyway it represents the size of the image when opened in RAM. That's an intersting piece of information.