Are 10 and 20 dollar bills the same size?

Answer 1

Regardless of denomination, all current US paper bills are the same size (155.96 mm x 66.29 mm) and weight (1 gram).

In many other countries, each bill is a different size as an anti-counterfeiting measure. Higher-denomination bills are larger which prevents counterfeiters from bleaching a low-value bill and reprinting it with a higher denomination. The US instead adds special hidden security strips to each denomination. The strips for each denomination are in different places and glow different colors under UV light.