When you need this calculator
Cropping a photo for a specific frame, setting a video export size, sizing a hero image so it doesn’t stretch, or checking whether a monitor’s resolution matches the ratio its box claims. The ratio tells you the shape; the resize field tells you the missing side.
How the ratio is found
The calculator finds the greatest common divisor (GCD) of the width and height, the largest number that divides both exactly, and divides both sides by it. For 1920 × 1080 the GCD is 120, giving 16:9. Decimal sizes (for example 1.5 × 1 m) are scaled up to whole numbers first.
If the reduced ratio still has large numbers, like 1921 × 1080, the ratio is shown as a decimal (1.779:1) instead of a fraction nobody could use, alongside the nearest standard.
Common ratios
- 16:9: HD and 4K video, most monitors and TVs.
- 4:3: classic TV, iPad, many compact cameras.
- 3:2: 35 mm film and most DSLR and mirrorless sensors.
- 16:10 (8:5): many laptop displays.
- 1:1, 4:5, 9:16: social feeds, portrait posts and vertical video.
Common mistakes
Rounding the resized side down. 1920 × 1080 at 1000 wide is 562.5 high. Round to 563, not 562, or you’ll crop a row off the image.
Mixing up width and height. 9:16 and 16:9 are the same shape turned on its side. Check which one your platform expects.