How to use this calculator
Enter the requested values, review any options that affect the calculation, and select Calculate. The main answer appears beside the form, with supporting details below it.
How the calculation works
Ratios are simplified by dividing both terms by their greatest common divisor. Proportions are solved by cross multiplication.
Example
20:30 simplifies to 2:3. In 3/5 = x/20, x is 12.
Related calculators
Frequently asked questions
Can any value be unknown?
Yes. In proportion mode, leave exactly one of A, B, C, or D blank.