Simplify a resolution into a ratio, or solve for a missing width/height.
The calculator divides both numbers by their greatest common divisor. 1920 and 1080 share 120, so the ratio becomes 16:9. That is the whole method β there is no table of known ratios to match against, which is why unusual sizes still reduce correctly.
When you give a ratio and one side, it solves the other side from width Γ· height = ratio and rounds to a whole pixel. Rounding is where a one-pixel difference can appear: 1365Γ768 is 16:9 to three decimals but does not reduce to 16:9 exactly.
| Pixels | Ratio | Width Γ· height |
|---|---|---|
| 1920Γ1080 | 16:9 | 1.778 |
| 1280Γ720 | 16:9 | 1.778 |
| 3840Γ2160 | 16:9 | 1.778 |
| 1080Γ1080 | 1:1 | 1.000 |
| 1080Γ1920 | 9:16 | 0.562 |
| 2560Γ1080 | 64:27 | 2.370 |
| 1440Γ1080 | 4:3 | 1.333 |
| 4096Γ2160 | 256:135 | 1.896 |
Two sizes can share a ratio label and still not scale into each other without rounding. The decimal column is the honest comparison β if two sizes have the same decimal, one scales into the other exactly.
2560Γ1080 reduces to 64:27, not to a tidy number, because ultrawide displays were defined by their diagonal rather than by a simple whole-number ratio. The preview box above scales the rectangle to fit while keeping the decimal, so what you see is the real shape.
Both numbers are divided by their greatest common divisor. 1920 and 1080 share 120, giving 16:9.
Because it is only close. 1365Γ768 is 16:9 to three decimals but does not divide evenly.
2560Γ1080 reduces to 64:27. Ultrawide sizes were defined by diagonal rather than by a simple ratio.
When solving for a missing side, yes β to a whole pixel. That can leave a one-pixel difference.
Do not use the rounded result for print or video masters without checking the target spec; a one-pixel difference can force a rescale.
Free online aspect ratio calculator. Simplify width and height into a ratio like 16:9, or enter a ratio plus one dimension to find the other. Includes a visual preview.
Reducing a resolution to a ratio is the same operation as simplifying a fraction: divide both numbers by their greatest common divisor. For 1920 Γ 1080 the greatest common divisor is 120, and 1920 Γ· 120 = 16 while 1080 Γ· 120 = 9 β hence 16:9.
The reduction is why very different resolutions share one ratio. 1920Γ1080, 1280Γ720 and 3840Γ2160 all reduce to 16:9, so a video mastered at any of them fills the same frame with no bars.
| Resolution | Reduces to | Decimal |
|---|---|---|
| 1920 Γ 1080 | 16:9 | 1.7778 |
| 1280 Γ 720 | 16:9 | 1.7778 |
| 3840 Γ 2160 | 16:9 | 1.7778 |
| 1024 Γ 768 | 4:3 | 1.3333 |
| 1080 Γ 1350 | 4:5 | 0.8000 |
| 2560 Γ 1080 | 64:27 | 2.3704 |
The last row is the one that surprises people. A monitor sold as β21:9β is usually 2560Γ1080 or 3440Γ1440, which reduce to 64:27 and 43:18 β neither is exactly 21:9 (2.3333). The marketing name is rounded; the decimal is what the frame actually does.
Two ratios written differently can be nearly identical in practice, and two that look similar can be noticeably different. Comparing decimals settles it: 1.7778 against 1.3333 is a visibly different frame, while 2.3704 against 2.3333 is a sliver at the edges. When you need to know whether content will letterbox, compare the decimals rather than the labels.
If the source and target ratios differ you have three honest options, and one that looks wrong. Letterbox adds bars above and below when the source is wider than the target. Pillarbox adds bars at the sides when the source is taller. Crop fills the frame and loses the edges. Stretching to fit changes the decimal, so circles become ovals and faces widen β that is the one to avoid.
To resize without changing the ratio, solve for the missing side: new height = new width Γ· decimal. A 16:9 clip at 1500 px wide needs a height of 1500 Γ· 1.7778 = 843.75, so 844 px, and the half-pixel is why encoders prefer even numbers.
Common chroma subsampling schemes store colour at half resolution horizontally and vertically, so each colour sample covers a 2Γ2 block of pixels. An odd width or height leaves an incomplete block, and many encoders refuse it or pad silently.
It reduces to 4:5, the portrait ratio used by several social feeds. It is standard in that sense, but it is not a broadcast or cinema ratio.
Only with older or anamorphic formats where stored pixels are not square. For everything square-pixel, the frame ratio and the stored resolution ratio are the same number.
Ratios are conventions attached to a delivery format, so the right one is decided by where the frame will be watched rather than by preference. Broadcast and most online video are 16:9. Cinema uses two widescreen standards: 1.85:1, which is close to 16:9 and fills a modern screen almost exactly, and 2.39:1, the wider βscopeβ frame that letterboxes on a 16:9 display. Vertical feeds are 9:16, the inverse of broadcast, and square posts are 1:1.
Still photography keeps its own: 3:2 comes from 35 mm film and is what most interchangeable-lens cameras shoot, while 4:3 is the native ratio of many phone sensors and of micro four-thirds. Printing crops again β a 4Γ6 inch print is 3:2 and matches a camera frame, but 5Γ7 is 1.4:1 and 8Γ10 is 1.25:1, so both cut the long edge off a 3:2 photograph.
| Use | Ratio | Decimal |
|---|---|---|
| Broadcast and online video | 16:9 | 1.7778 |
| Cinema, standard widescreen | 1.85:1 | 1.8500 |
| Cinema, scope | 2.39:1 | 2.3900 |
| Vertical video | 9:16 | 0.5625 |
| Square post | 1:1 | 1.0000 |
| 35 mm stills | 3:2 | 1.5000 |
| Phone and MFT sensors | 4:3 | 1.3333 |
Shooting in the delivery ratio avoids a decision later. Shooting wider than the delivery ratio leaves room to reframe, at the cost of resolution in whatever you crop away.