صورة:BauxiteUSGOV.jpg

This image has currency in it to indicate scale.

Avoid using objects such as coins for scale, as they will require people unfamiliar with them to look up the dimensions or guess, both of which defeat the purpose of the object in the first place. Coins are particularly bad as they can reinforce a geographical bias, and some coins' designs are not free content.

Ideally, a photograph should include a ruler with the subject or add a scale marking via an image editor instead. SI/metric units are the most commonly used worldwide (see metre, 1 E-2 m).

Examples of good practice: with (metric & imperial) ruler and with superimposed line.
Examples of bad practice: here.

• U.S. dollar:
  • 1¢: 19 mm, 0.75 in
  • 5¢: 20 mm, 0.79 in
  • 10¢: 18 mm, 0.71 in
  • 25¢: 24 mm, 0.95 in
  • 50¢: 31 mm, 1.21 in
  • $1: 26 mm, 1.02 in

• Canadian dollar:
  • 1¢: 19 mm, 0.75 in
  • 5¢: 21 mm, 0.83 in
  • 10¢: 18 mm, 0.71 in
  • 25¢: 24 mm, 0.94 in
  • 50¢: 27 mm, 1.07 in
  • $1: 26 mm, 1.04 in
  • $2: 28 mm, 1.10 in

• Pound sterling
  • 1p: 20.32 mm, 0.80 in
  • 2p: 25.91 mm, 1.02 in
  • 5p: 18.00 mm, 0.71 in
  • 10p: 24.50 mm, 0.96 in
  • 20p: 21.40 mm, 0.84 in
  • 50p: 27.30 mm, 1.07 in
  • £1: 22.50 mm, 0.89 in
  • £2: 28.40 mm, 1.12 in

• Euro
  • 1c: 16.25 mm, 0.64 in
  • 2c: 18.75 mm, 0.74 in
  • 5c: 21.25 mm, 0.84 in
  • 10c: 19.75 mm, 0.78 in
  • 20c: 22.25 mm, 0.88 in
  • 50c: 24.25 mm, 0.95 in
  • €1: 23.25 mm, 0.92 in
  • €2: 25.75 mm, 1.01 in