How the calculation works
An aspect ratio is just the proportion between width and height, written as two numbers like 16 : 9. To keep that proportion when you change one side, the other side has to scale by the same factor.
The calculator takes the dimension you already know and multiplies it by the ratio of the two ratio numbers. If you know the width and want the height, it computes height = width × ratioHeight ÷ ratioWidth; solving for width flips the fraction.
Reading the simplified ratio
Alongside the solved dimension, the tool shows the ratio reduced to its smallest whole numbers by dividing both sides by their greatest common divisor.
- 1920 : 1080 reduces to 16 : 9, the standard widescreen shape.
- 1280 : 1024 reduces to 5 : 4, an older monitor proportion.
- A simplified ratio makes it easy to spot whether two sizes share the same shape.
Practical uses
Aspect ratios come up whenever you resize an image, set a video resolution, or fit content into a frame without stretching it.
- Find the height for a banner when only the target width is fixed.
- Check that a cropped photo still matches a print size like 3 : 2.
- Plan video exports for 16 : 9, 9 : 16 vertical, or 1 : 1 square layouts.
Common mistakes
Mixing up which side you are solving for is the usual slip. Confirm that the known value is the one you actually have, and that the ratio numbers are in width-then-height order.
Results may not land on whole pixels. Rounding to the nearest integer is fine for display, but check that the chosen value is supported by your screen or codec.
Formula
height = known × ratioH ÷ ratioW; width = known × ratioW ÷ ratioHFrequently asked questions
- What does the simplified ratio mean?
- It divides both sides by their greatest common divisor, so 1920 by 1080 simplifies to 16 by 9.