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In typical [[image compression|uncompressed]] bitmaps, image [[pixel]]s are generally stored with a variable number of bits per pixel which identify its color (the [[color depth]]). Pixels of 8 bits and fewer can represent either [[grayscale]] or [[indexed color]]. An [[alpha channel]] (for [[transparency (graphic)|transparency]]) may be stored in a separate bitmap, where it is similar to a grayscale bitmap, or in a fourth channel that, for example, converts 24-bit images to 32 bits per pixel.
The bits representing the bitmap pixels may be [[packed]] or unpacked (spaced out to byte or word boundaries), depending on the format or device requirements. Depending on the color depth, a pixel in the picture will occupy at least ''n''/8 bytes, where {{Var|n}} is the bit depth.
For an uncompressed, packed-within-rows bitmap, such as is stored in Microsoft DIB or [[BMP file format]], or in uncompressed [[TIFF]] format, a lower bound on storage size for a ''n''-bit-per-pixel (2<sup>n</sup> colors) bitmap, in [[byte]]s, can be calculated as:
:<math>\text{size} = \text{width} \cdot \text{height} \cdot n/8</math>
where width and height are given in pixels.
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