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This may be a Math. How to calculate this.
You cannot calculate it using Canvas Size as shown, because to work out the file size, you must know how the pixel dimensions of the image, so Width and Height must be set to pixels.
I determined the specs using Image Size. If a document of those dimensions in cm is set to 72 ppi, then it will have a 51.3MB file size if it is set to 8 bits per channel.
The math is not specific to Photoshop, it works in all digital image editing in any application. If compression and layers are not involve
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Photoshop's native unit is the pixel. Physical sizes are derived from whatever ppi (pixels per inch) number is assigned. Ppi is a way to translate from pixels into physical measurements, but Photoshop itself works only with pixels.
If you get into the habit of thinking in pixels and setting up your documents by pixels, everything becomes much simpler. Then megapixel count is just width x height.
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There are many YouTube videos about canvas & Image size but those are conviently slient about calculating the size.
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You cannot calculate it using Canvas Size as shown, because to work out the file size, you must know how the pixel dimensions of the image, so Width and Height must be set to pixels.
I determined the specs using Image Size. If a document of those dimensions in cm is set to 72 ppi, then it will have a 51.3MB file size if it is set to 8 bits per channel.
The math is not specific to Photoshop, it works in all digital image editing in any application. If compression and layers are not involved, the file size is always:
Number of pixels wide
times
Number of pixels tall
times
Bits per channel
times
Number of channels
If a document is
182.88cm wide
121.92cm tall
set to
72 ppi
then it is
5184 x 3456 px
which equals
143,327,232 bits
times 3 RGB channels, which equals
429,981,696 bits, which equals 53,747,712 bytes,
or around 54MB
…which is close to the file size shown at the top of your Canvas Size screen shot.
(I haven’t worked out why it’s more than your 51.3MB unless your actual pixel dimensions are different than my educated guess of 5184 x 3456 px)
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Thanks.