To cover the ten most traded currencies and ten most populous countries, the following are close in size to the coin in the post:
Australian dollar: 5 cent
Bangladeshi taka: 5 poisha
Brazilian real: slightly smaller than the 10 centavo
British pound: Between the 1 penny and the 5 pence
Canadian dollar: 1 cent
Chinese renminbi: 1 jiao
Euro: 2 cent
Hong Kong dollar: 20 cent
Indian rupee: 50 paise
Indonesian rupiah: slightly smaller than the 50 rupiah
Japanese yen: slightly smaller than the 1 yen
Mexican peso: 20 centavo
Nigerian naira: smaller than all current coins. About three-quarters the diameter of the 2 naira
Pakistani rupee: 5 rupee
Russian ruble: between the 5 kopeck and 50 kopeck
Singaporean dollar: 10 cent
Swiss franc: 10 centime