Aspect Ratio Calculator
Calculate the missing width or height to match an aspect ratio, simplify a ratio from pixel dimensions, or look up common screen resolutions.
Fill in either Width or Height (leave the other blank) along with the ratio — the missing dimension is calculated automatically. If both are filled, the height will be recalculated to match the ratio.
Common Resolutions & Ratios (click a row to load it)
| Name | Resolution | Ratio |
|---|
How to Use
- Choose a mode: "Calculate Dimension" or "Find Ratio".
- Calculate Dimension: enter a known width or height and a target aspect ratio (e.g. 16:9) to find the missing dimension.
- Find Ratio: enter a width and height to see the simplified aspect ratio (e.g. 1920×1080 → 16:9).
- Use the common resolutions table for quick reference — click any row to load those dimensions into the calculator.
- Results update instantly as you type — no need to click Calculate.
When to Use This
- Resizing a banner to a fixed width while keeping its proportions, where typing the width fills in the height that preserves the ratio.
- Checking whether an asset someone sent you is genuinely 16:9 before you drop it into a video timeline and discover black bars.
- Picking export dimensions for a vertical social post by loading a preset row and reading the simplified ratio it produces.
- Working out the height of an embedded player that has to fill a known container width at a chosen aspect ratio.
Frequently Asked Questions
About This Calculator
An aspect ratio is a proportion, not a size: 16:9 describes 1280 x 720 and 3840 x 2160 equally well. Reducing pixel dimensions to that proportion means dividing both numbers by their greatest common divisor, which is how 1920 x 1080 collapses to 16:9. Going the other way, a known ratio plus one dimension fixes the other by cross-multiplication, scaling the image without distorting it.
Dimension mode takes a ratio and whichever of width or height you typed in last, then computes the other and rounds it to two decimals. Find Ratio multiplies both numbers by 1000, rounds them to integers and divides by their greatest common divisor, so fractional inputs are handled down to three decimal places. A table of fourteen common resolutions sits below; clicking a row loads those numbers into both modes at once.
Notes & Limits
- The ratio is reduced by exact greatest common divisor rather than matched to the nearest familiar ratio, so 1366 x 768 reports 683:384, not the approximate 16:9.
- Calculated dimensions are rounded to two decimals and are not forced to whole or even pixel counts, which some video encoders require of their input.
- This computes numbers only. No image or video file is read, resized or exported; you apply the dimensions in an editor of your own.
- Fractional inputs are handled to three decimal places, because both numbers are multiplied by 1000 and rounded before the common divisor is taken.