Why is the Dime Smaller in Size than the Nickel and Penny?

By GovMint :

The dime is smaller than the nickel and penny due to its historical origins. When the U.S. Mint began producing coins in 1793, the standard was the silver dollar. During this time of American history, coins were made with a silver content proportional to the dollar, meaning a dime contained 1/10th the silver of a dollar, determining its smaller size. The original five-cent coin, actually referred to as a half dime or half disme, was made of silver and was even smaller in size than today's dime. However, it was deemed too small for practical use, leading to the creation of the larger nickel in 1866, made from a copper-nickel alloy instead of silver.

Sources Used:

https://www.factmonster.com/askeds/why-nickels-are-bigger-dimes