Aspect Ratio Calculator

How this is calculated

An aspect ratio is width divided by height. That decimal is the whole thing - 1920 by 1080 is 1.7778, and so is 1280 by 720, and so is any other 16:9 size. Two images match if and only if their decimals match. To resize without distorting, hold that decimal constant. Given a new width, the height is the new width divided by the ratio. Given a new height, the width is the height multiplied by the ratio. Those are the two outputs here, and you use whichever one your constraint is. ⚠️ THE DECIMAL IS MORE USEFUL THAN THE COLON NOTATION. 16:9 and 1.7778 say the same thing, but the decimal can be compared at a glance: 1.7778 against 1.5 tells you immediately which is wider, where 16:9 against 3:2 does not. It also works for ratios with no tidy whole-number form, which is most real images once they have been cropped. COMMON RATIOS as decimals: 16:9 is 1.7778 - video, most monitors, YouTube. 4:3 is 1.3333 - older screens, many camera sensors, iPads. 3:2 is 1.5 - most DSLR and mirrorless photos, and 6x4 prints. 1:1 is 1.0 - square. 9:16 is 0.5625 - vertical video, Stories, Reels. 21:9 is about 2.3333 - ultrawide monitors, though cinema's 'scope' formats are nearer 2.39. THIS IS WHY YOUR PHOTOS GET CROPPED. A camera shooting 3:2 at 1.5 and a phone screen at 0.5625 are not close, so something has to go. The same mismatch is behind photos cropped by print sizes: a 6x4 print is 1.5 and matches a DSLR exactly, while a 5x7 is 1.4 and an 8x10 is 1.25 - both of which cut your image, which is why the 8x10 of a group photo loses people at the edges. UPSCALING DOES NOT ADD DETAIL. Doubling both numbers keeps the ratio perfectly and adds nothing to the image; the arithmetic is happy and the picture is soft. Getting a ratio right and getting an image sharp are different problems. The pixel count output is here as a reminder that area grows with the SQUARE of the scale. Doubling both dimensions quadruples the pixels, and often the file size with them.

Common questions

What is an aspect ratio, exactly?

Width divided by height, expressed as a single decimal. 1920 by 1080 gives 1.7778, and so does 1280 by 720, and 3840 by 2160 - they are all 16:9. That decimal is the entire concept: two images have the same shape if and only if their decimals match, whatever their pixel dimensions. Everything else about aspect ratios is notation for that one number.

Why prefer the decimal to 16:9?

Because you can compare decimals at a glance and you cannot compare colon notation. 1.7778 against 1.5 immediately tells you which is wider; 16:9 against 3:2 requires arithmetic first. The decimal also handles ratios that have no tidy whole-number form, which is most real images once they have been cropped even slightly. Colon notation is good for naming a standard and poor for working with an actual file.

How do I resize without distorting?

Hold the ratio constant. If the width is your constraint, the new height is your new width divided by the ratio. If the height is your constraint, the new width is the height multiplied by the ratio. This calculator shows both because in practice you are constrained by width about half the time - a content column, a banner slot - and by height the other half, in a header strip or a fixed-height row.

Why do my photos get cropped on my phone?

Because the shapes genuinely do not match. Most cameras shoot 3:2, a decimal of 1.5. A phone screen in portrait is 9:16, which is 0.5625. Those are nowhere near each other, so something has to be cut or letterboxed. The same mismatch explains print sizes: a 6x4 print is exactly 1.5 and matches a DSLR frame perfectly, while a 5x7 is 1.4 and an 8x10 is 1.25 - both crop your image, which is why an 8x10 of a group photo loses the people at the edges.

What is the percentage output for?

Height as a share of width is the number responsive layouts use. The long-standing CSS technique for reserving space for an image or embed before it loads sets a padding based on exactly this percentage - 56.25% for 16:9 - so the page does not jump when the media arrives. Modern CSS has aspect-ratio as a property, but the percentage still turns up in a great deal of existing code and in most embed snippets.

Does upscaling lose quality?

It does not add any, which amounts to the same thing. Doubling both dimensions preserves the ratio perfectly and produces an image with four times the pixels and exactly as much detail as before - the extra pixels are interpolated from the ones you had. The arithmetic here will happily tell you the correct enlarged dimensions; whether the result looks acceptable is a separate question this cannot answer. Getting a ratio right and getting an image sharp are different problems.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Aspect Ratio Calculator at https://www.bfcbrilliance.com/tools/aspect-ratio-calculator.

What I entered:
- Original width (px): ___
- Original height (px): ___
- New width (if width is your constraint) (px): ___
- New height (if height is your constraint) (px): ___

What it calculated:
- Height at your new width: ___
- Width at your new height: ___
- Aspect ratio: ___
- Height as a share of width: ___
- Scale factor at your new width: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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