If you know the location of the image then you can do the following:
FileInfo imageInfo = new FileInfo(imagePath);
int sizeInBytes = imageInfo.Length;
if you are creating the image yourself and you know the width and height in pixels aswell as the colour depth then you can use the following formula to work out the size of the image in kilobytes.
Division by 8 will give you an answer in bytes
Division by 8*1024 will give you an answer in Kb
Division by 8*1024*1024 will give you an answer in Mb
width in pixels × height in pixels × colour depth
SizeInKb = ___________________________________________________
8 × 1024
The following is a table of colour depth
Colour Depth in Bits Number of Colours Number of Colours calculations
1 2 2^1 = 2
2 4 2^2 = 4
3 8 2^3 = 8
4 16 2^4 = 16
5 32 2^5 = 32
6 64 2^6 = 64
7 128 2^7 = 128
8 256 2^8 = 256
16 65536 2^16 = 65563
24 16777216 2^24 = 16777216
32 4294967296 2^32 = 4294967296
etc
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