Part-to-whole, not part-to-part
This calculator treats the second value as the whole. If your ratio is part-to-part, add the parts together first to get the whole.
Example
If 3 students out of 8 choose an option, the share is 3 / 8 x 100 = 37.5%.
Common mistakes
For a ratio written 3:5, the whole is usually 8 if you want the first part's share of the total. Entering 3 as the part and 5 as the whole answers a different question.
When not to use it
Use percentage change instead when you compare an old value with a new value. Ratio-to-percent is for a part as a share of a total.
Last reviewed: 2026-05-17