Ratio Calculator

Solve A : B = C : D, simplify ratios, compare two ratios and list equivalent ratios.

How do I solve a ratio or proportion?

Enter A and B and leave C or D empty to solve the proportion A : B = C : D by cross-multiplication — for example 16 : 9 = 1920 : 1080. Enter only A and B to simplify the ratio, or all four numbers to check whether two ratios are equal.

How it works

In a proportion A : B = C : D, A × D = B × C, so D = B × C ÷ A. Ratios are simplified by dividing both parts by their greatest common divisor.

Everyday uses

Scaling recipes and mixtures (2 : 3 concrete or paint ratios).
Resizing images and videos while keeping the aspect ratio.
Maps and model scales.

Frequently asked questions

Can I use decimals?

Yes, decimals are supported and simplified.

Is this the same as the aspect ratio calculator?

This is a general ratio solver; the aspect ratio calculator is specialised for widths and heights.

Is it free?

Yes.