Ratio Calculator
Simplify to lowest terms — then scale to any size that keeps it true.
How this is calculated
simplified = (a ÷ gcd) : (b ÷ gcd) · scaled right = new-left × b ÷ a
Worked example: 1920:1080 has GCD 120, so it simplifies to 16:9 — the video standard. Scaling that to 1280 on the left gives 720 on the right: the familiar 1280×720. Ratios are unitless, so the same page settles screens, print sizes, map scales, and two-part mixes alike.
Frequently asked questions
How does the ratio simplifier work?
It divides both numbers by their greatest common divisor: 1920:1080 ÷ 120 = 16:9. The GCD comes from Euclid’s algorithm, printed below with the worked example.
How do I scale a ratio to a new size?
Enter the ratio and the one known new value — the calculator finds the other side so the proportion holds. A 16:9 image at 1280 wide needs 720 high; the scaling row answers exactly that live.
What are common screen and photo ratios?
16:9 (video, monitors), 4:3 (older screens, iPads), 3:2 (photos, many laptops), 1:1 (square posts), 9:16 (vertical video), 21:9 (ultrawide). Simplifying pixel dimensions is the quickest way to identify which one you have.
Does it work for recipes and mixing?
Yes — ratios are unitless. A 2:3 mix scaled to 500 of the second part needs 333.3 of the first; the scaling row handles the decimals that kitchen and workshop mixes actually produce.