• Size of bitmap = no. of Horizontal pixels X no. of Vertical pixels X Colour Depth
• No. of pixels = DPI X size in inches

You should also be able to convert from bits, Bytes, Kilobytes, Megabytes, Gigabytes & Terabytes.

• Bit= 1/0 (Binary digIT)
• 1 Byte = 8 Bits
• 1 Kilobytes= 1024 Bytes  (2¹⁰)
• 1 Megabytes= 1024 KB  (2²⁰)
• 1 Gigabytes = 1024 MB  (2³⁰)
• 1 Terabytes = 1024 GB  (2⁴⁰)

For colour depth

• 8 bits = 256 colours (2⁸)
• 16 bits = High Colour 65,536 colours (2¹⁶)
• 24 bits = True Colour 16,777,216 colours (2²⁴)