Finally, here is a quick reference so that you won't have to go through the mathematical gyrations to find out how tall an action figure should be. For example, if you wanted to customize a 5" scale Captain America (character is 6' 2" tall), you could use the table below to help find an appropriate base figure. Look in the 5" scale column until you find something close to 6' 2". As you can see, a base figure that is 5 1/8 inches tall would work very well. Similarly, for a 5" scale Thor (character is 6' 6" tall), a base figure between 5 3/8 and 5 1/2 inches tall would be in correct scale.

Using Web Traps Spiderman:
Figure height = 5.5 in
Reference height = 5 ft, 10 in = 5.83 ft

Scale calculation:
true scale = fig height / ref height = (5.5 in / 5.83 ft) = 0.943 in/ft
action figure scale = true scale x 6 ft = (0.943 in/ft) x (6 ft) = 5.7" scale

Reference error calculations:
ref error = (fig height * fig scale) - ref height

[5" scale]
ref error = (5.5 in * (6 ft / 5 in)) - 5.83 ft = 0.77 ft = +9 inches error

[5.5" scale]
ref error = (5.5 in * (6 ft / 5.5 in)) - 5.83 ft = 0.17 ft = +2 inches error

[6" scale]
ref error = (5.5 in * (6 ft / 6 in)) - 5.83 ft = -0.33 ft = -4 inches error