Aspect Ratio Calculator
Find the missing width or height that keeps an aspect ratio, or simplify any width×height to its lowest terms, with the nearest standard format named.
Aspect Ratio Calculator: with the default inputs, missing dimension is 1,440.
Any unit works — pixels, millimetres, inches — as long as both sides use the same one.
The width you are scaling to (or the height, in width mode). Ignored when simplifying.
The height or width that preserves the ratio. Ignored in simplify mode, which returns the original height.
- Aspect ratio
- 16:9
- Ratio as a decimal (width ÷ height)
- 1.7778
- Scaled size
- 2,560 × 1,440
- Nearest standard format
- 16:9 (1.7778) — exact match
- Scale factor
- 1.3333
- Rounded to whole pixels
- 2560 × 1440
- Scaled megapixels
- 3.686
Assumptions
- Square pixels — the pixel dimensions are the display shape. Anamorphic material needs its display aspect ratio instead.
- Ratios are simplified only when both dimensions are whole numbers.
- The nearest standard format is chosen by the smallest proportional difference, not the smallest absolute one.
| Ratio | Decimal | At 2,560 px wide | Where you see it |
|---|---|---|---|
| 1:1 | 1 | 2560 × 2560 | Square — Instagram posts, profile pictures |
| 5:4 | 1.25 | 2560 × 2048 | 8×10 print, old 1280×1024 monitors |
| 4:3 | 1.3333 | 2560 × 1920 | Classic TV, iPad, most compact-camera sensors |
| 3:2 | 1.5 | 2560 × 1707 | 35 mm film, DSLR sensors, 4×6 prints |
| 16:10 | 1.6 | 2560 × 1600 | Many laptops and productivity monitors |
| 5:3 | 1.6667 | 2560 × 1536 | Super 16 mm, some projectors |
| 16:9 | 1.7778 | 2560 × 1440 | HDTV, YouTube, 1080p and 4K UHD |
| 1.85:1 | 1.85 | 2560 × 1384 | Standard cinema widescreen |
| 2:1 | 2 | 2560 × 1280 | Univisium — a lot of streaming originals |
| 21:9 | 2.3704 | 2560 × 1080 | Ultrawide monitors (2560×1080, 3440×1440) |
| 2.39:1 | 2.39 | 2560 × 1071 | Anamorphic scope — the widest common cinema format |
| 9:16 | 0.5625 | 2560 × 4551 | Vertical video — Reels, Shorts, TikTok |
21:9 is a marketing name, not arithmetic — real ultrawide panels are 64:27 (2.37) or 43:18 (2.39). 2560×1080 is actually 2.370:1.
How this is worked out
The formula
Aspect ratio = width ÷ height New height = new width ÷ ratio New width = new height × ratio Simplified form: divide both by GCD(width, height) 1920 ÷ 120 = 16, 1080 ÷ 120 = 9 → 16:9
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- What do you need?
- Choose one of 3 options.Height for a new width · Width for a new height · Just simplify this ratio
- Original width
- Any unit works — pixels, millimetres, inches — as long as both sides use the same one.0 or more · defaults to 1920
- Original height
- A number.0 or more · defaults to 1080
- New dimension
- The width you are scaling to (or the height, in width mode). Ignored when simplifying.0 or more · defaults to 2560
What you get back
- Missing dimensionmain answer
- The height or width that preserves the ratio. Ignored in simplify mode, which returns the original height.
- Aspect ratio
- Ratio as a decimal (width ÷ height)
- Scaled size
- Nearest standard format
- Scale factor
- Rounded to whole pixels
- Scaled megapixels
What this assumes
- Square pixels — the pixel dimensions are the display shape. Anamorphic material needs its display aspect ratio instead.
- Ratios are simplified only when both dimensions are whole numbers.
- The nearest standard format is chosen by the smallest proportional difference, not the smallest absolute one.
About this calculator
Aspect ratio is width divided by height, and almost every image or video problem that ends in unexpected black bars or a squashed logo is a ratio that changed somewhere in the pipeline. This resizes one dimension while keeping the ratio fixed, or reduces a size you already have to its lowest terms and tells you which standard format it is closest to.
Reading a ratio
16:9 means 16 units across for every 9 down, i.e. 1.778 wide as tall. To simplify a resolution, divide both numbers by their greatest common divisor: 1920 and 1080 share 120, giving 16:9. 2560×1440 shares 160, also 16:9 — which is why a 1440p video fills a 1080p frame exactly.
Cinema uses a different convention: a single decimal against 1, so "1.85:1" and "2.39:1". They are the same idea written differently — 16:9 is 1.78:1.
The ratios that are lying to you
- 21:9 is not 21:9. Ultrawide monitors are actually 64:27 (2.370) or 43:18 (2.389). 2560×1080 divides to 64:27. The marketing name is rounded, and if you author content at literally 21 ÷ 9 = 2.333 it will not fit the panel.
- Anamorphic footage stores non-square pixels. A 720×480 DVD frame is not 3:2; it is 4:3 or 16:9 depending on a flag in the file. Check the display aspect ratio, not the pixel dimensions.
- "4K" is two different shapes. UHD (3840×2160) is 16:9; DCI 4K (4096×2160) is 1.90:1. They are not interchangeable.
Rounding, and why encoders hate you
Scaling rarely lands on whole pixels: 1920×1080 scaled to 1000 px wide gives 562.5 high. You have to round, and rounding changes the ratio slightly. Worse, H.264 and H.265 require even dimensions — 563 will be rejected or silently padded by most encoders, and many prefer multiples of 4 or 16 to line up with macroblocks. When the calculator warns about odd dimensions, take the warning: round to an even number and accept a ratio error in the third decimal place.
Fitting one ratio inside another
When the source and target ratios differ you must choose what to sacrifice:
- Letterbox / pillarbox — fit the whole frame and add bars. Nothing is lost.
- Crop — fill the frame and lose the edges. Fine for backgrounds, fatal for text and faces near the border.
- Stretch — never. It is instantly visible on anything with a circle or a face in it.
For social media, design to the tightest crop that any platform will apply, then keep everything important inside that safe area.
Frequently asked questions
▸What is the aspect ratio of 1920×1080?
16:9. Both numbers divide by 120, giving 16 and 9, which as a decimal is 1.778 wide as it is tall.
▸How do I resize an image without distorting it?
Pick one dimension and derive the other from the ratio: new height = new width ÷ (original width ÷ original height). Changing both independently is what squashes the picture.
▸Is 21:9 really 21:9?
No. Ultrawide panels are 64:27 (2.370) or 43:18 (2.389). 2560×1080 and 3440×1440 both work out to 64:27 — '21:9' is a rounded marketing label.
▸Why does my video get rejected for odd dimensions?
H.264 and H.265 encode in blocks and require both dimensions to be even; many workflows want multiples of 4 or 16. Round your scaled size to an even number of pixels.
▸What is the difference between 4:3 and 16:9?
4:3 (1.333) is the old TV and monitor shape; 16:9 (1.778) is the modern video standard. Showing 4:3 material on a 16:9 screen leaves vertical bars at the sides — that is pillarboxing, and it is correct behaviour.
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