Aspect Ratio Calculator
Simplify any width × height to its exact ratio, solve a missing dimension at a locked ratio, or drop an image to read its size. Honest to the pixel: 1366×768 is reported as ≈16:9, not 16:9.
1 · Size → ratio
2 · Solve a missing side
Ratio
Solved size
Everything runs on your device. The ratio math is plain integer arithmetic in this tab, and a dropped image is read locally only to get its width and height — no uploads, no server, works offline.
How the ratio is computed — and why this tool won't lie to you
The simplified ratio is exact arithmetic: divide both sides by their greatest common divisor. 1920 and 1080 share a GCD of 120, so 1920×1080 is 16:9; 1280 and 1024 share 256, so 1280×1024 is 5:4 — not the 4:3 it is often mistaken for (4:3 at 1280 wide would be 1280×960). The decimal form is just width ÷ height rounded to two decimals: 16:9 → 1.78:1.
The honesty is in the third line. Many sizes are near a famous ratio without being it: 1366×768, the most common laptop resolution of the 2010s, simplifies to 683:384, which is 0.048828125% wider than 16:9. Most calculators silently print “16:9”; this one prints ≈16:9 (off by 0.05%) and keeps the exact ratio on top. That distinction is not pedantry — scale a “16:9” video frame onto a 1366×768 panel and the mismatch is exactly where the one-pixel letterbox line comes from. If nothing in the common list is within 3%, the tool says so instead of stretching a label.
Solving a missing side, with the rounding rule stated
Lock a ratio and enter the side you know: the other is known × ratio, computed live. Ratios rarely divide evenly into whole pixels, so a rule is unavoidable — this tool rounds to the nearest whole pixel, halves round up, never below 1 px, and tells you when it happened. Worked example: 16:9 at width 1000 gives 1000 × 9 ÷ 16 = 562.5, which rounds to 563. Going back, 563 px of height at 16:9 asks for 1000.9 of width → 1001: round-trips can drift by a pixel, which is the honest cost of whole-pixel output, not a bug.
| Ratio | Width 1000 → height | Exact value |
|---|---|---|
| 16:9 | 563 | 562.5 (rounded up) |
| 4:3 | 750 | 750 (exact) |
| 21:9 | 429 | 428.571… |
| 2.39:1 | 418 | 418.410… |
The sizes table in the result pane is derived the same way — standard long-side lengths (1280, 1920, 2560, 3840) run through the ratio math on the spot, with rounded rows marked ≈. Nothing in it is a hard-coded claim.
Honest limits
“21:9” is a marketing name: real ultrawide panels are usually 2560×1080 or 3440×1440, which simplify to 64:27 and 43:18 — near, but not equal to, 21:9. The preset here is the literal 21:9; type an actual panel size into the ratio reader and it tells the truth (a 2560×1080 panel is in fact closer to cinemascope 2.39:1, off by 0.82%, than to 21:9, off by 1.59%). The image drop reads pixel dimensions only — it ignores EXIF rotation metadata, so a phone photo stored sideways reports its stored width×height, and it can't read HEIC because browsers can't decode it (convert to JPG first). This tool also does math on pixels, not physical units: for print sizes at a given DPI, pair it with the unit converter; to actually resize or crop to the numbers you solved, use the image resizer or crop tool.