What this does
Two jobs. The Original size pair turns any width and height
into its smallest whole-number ratio — 1920 × 1080 becomes
16:9 — and shows the same thing as a decimal,
1.778 : 1. The Scale pair below then solves for
whichever side you did not type, holding that ratio. Six presets (16:9, 4:3,
21:9, 3:2, 1:1, 9:16) fill the top pair in one click. It is all arithmetic in
the page — nothing is uploaded, and it works with the network off.
How do I resize an image without stretching it?
- Put the current width and height into Original size, or hit a preset if you already know the ratio.
- Check the reduced ratio shown between the two rows.
- Type your target width in the Scale row — the height fills itself in. Type a height instead and the width is solved the same way.
Both directions use the reduced ratio: height = width × h ÷ w, and width = height × w ÷ h. At 16:9, a width of 1920 gives 1080; at 4:3, a width of 800 gives 600.
How is the ratio itself reduced?
By greatest common divisor. Width and height are rounded to whole pixels, then both are divided by their GCD, found with Euclid's algorithm. For 1920 and 1080 the GCD is 120, which is where 16:9 comes from. 1024 × 768 divides down to 4:3, and any square — 500 × 500 — collapses to 1:1. Zero or negative numbers have no ratio, so the readout falls back to a dash.
What are the common aspect ratios and their resolutions?
Six shapes cover almost everything on a screen, and each preset here matches one of them:
| Ratio | Example sizes | Where it shows up |
|---|---|---|
| 16:9 | 1280 × 720, 1920 × 1080, 3840 × 2160 | HD and 4K video, most monitors, YouTube |
| 4:3 | 640 × 480, 1024 × 768, 2048 × 1536 | Older displays, slide decks, iPad screens |
| 3:2 | 1500 × 1000, 6000 × 4000 | Most DSLR and mirrorless photos |
| 21:9 | 2560 × 1080, 3440 × 1440 | Ultrawide monitors, cinematic crops |
| 1:1 | 1080 × 1080 | Square social posts, avatars |
| 9:16 | 1080 × 1920 | Reels, Shorts, TikTok, phone wallpapers |
Why does 3440 × 1440 come out as 43:18, not 21:9?
Because 43:18 is the true reduced ratio — the GCD of 3440 and 1440 is 80, and 43 is prime. "21:9" is a marketing label covering a family of near-ultrawide shapes; 2560 × 1080 really is 64:27. The tool always reports the exact reduced pair, so if you want the marketed shape, click the 21:9 preset instead of typing the panel's native resolution.
Why does the scaled side show decimals?
Not every target size lands on a whole pixel. Results are rounded to three decimal places rather than silently truncated, so 16:9 at a width of 1000 reads 562.5 — round it yourself to 562 or 563 when you export. The decimal line next to the ratio is the same idea in another form: 1.778 : 1 is 16 ÷ 9.
What should I do with the numbers?
Feed them to the image resizer to produce the file, or image crop when the source is the wrong shape and something has to go. For unit conversions such as inches to pixels at a given DPI, see unit converter.