Aspect Ratio Calculator
Type a width and a height to get the simplest ratio, then scale it to a new size without stretching the picture. Nothing is uploaded — there is no file here at all.
Aspect ratio
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Scale it, keeping this shape
Fill in one side. The other is worked out from the ratio above.
Near 16:9 is not 16:9
A calculator that answers “16:9” to 1918 x 1080 has rounded your picture into a shape it does not have. This one reduces your two numbers by their greatest common divisor and prints that, then names the nearest standard separately, with the percentage it is off by and a plain sentence saying it is not that ratio.
There is no file here
This tool takes two numbers and does arithmetic on them in your browser. Nothing is uploaded, nothing is stored and no account is needed, because there is nothing to upload in the first place. If you want the dimensions read out of an actual image, our Image Resizer and Pixel Ruler do that locally too.
How it works
The ratio comes from the greatest common divisor
A ratio is just your two numbers with everything common taken out of them. 1920 and 1080 share a divisor of 120, so the pair becomes 16 and 9 and the shape is written 16:9. That is the whole calculation, and it is done on the numbers you typed rather than on a lookup table of famous resolutions — which is why an odd size like 1366 x 768 comes back as 683:384 instead of being quietly filed under 16:9, the shape it is close to but does not have.
The nearest standard is labelled as nearest
Underneath the ratio, the closest common shape is named — 16:9, 4:3, 9:16 and the rest — together with how far your numbers sit from it as a percentage. When the match is exact the page says so in those words. When it is not, the page names the distance and then says outright that your picture is not that ratio. Both halves matter: the nearest standard is useful for deciding what to export, and it becomes a lie the moment it is printed as though it were the measurement.
Scaling shows the exact number, not just the rounded one
Hold 16:9 and ask for a width of 1000 and the honest height is 562.5. Pixels do not come in halves, so the usable answer is 563 — but 1000 x 563 is 1.7762:1, not 1.7778:1, and the picture has moved a fraction off the shape you asked for. The exact value is printed first, the whole-pixel pair second, and a line says whether the rounding changed the shape. Most calculators show you the rounded pair alone and let you assume the ratio survived it.
A number that is not whole does not get a whole-number pair
If you type 1920.5 x 1080 — which happens when a figure has come out of a layout tool rather than an image — there is no honest 16-and-9-style pair to give you, because the greatest common divisor is an operation on whole numbers. The page shows the decimal form instead and says why. Inventing a tidy whole-number pair for a measurement that was not whole would be reporting a shape you never typed, which is the same class of mistake as rounding a near miss up to a standard.