“Resize without losing quality” hides two very different jobs. Making an image smaller is nearly lossless when done right — and most tools do it wrong anyway. Making an image bigger cannot truly be lossless, but there are rules for how far you can push it. This guide covers both, plus the DPI question that confuses everyone.
The rules that matter
- Always resize from the original. Every save-as-JPG loses a little; resizing a resize compounds it. Keep the original, derive every size from it.
- Downscale freely, upscale reluctantly. Shrinking keeps quality; enlarging beyond ~1.5–2× shows. If you need big and the source is a logo or icon, get the SVG and render it at size instead.
- Resize to the exact target size. If the destination shows 1080×1350, deliver 1080×1350 (or exactly 2× for HiDPI). Delivering “roughly big enough” means the destination rescales again with whatever fast filter it has.
- Keep the aspect ratio unless you crop. Stretching to force a size distorts; the honest options are fit (letterbox), fill (crop), or a deliberate crop you control.
Exact pixels, inches/cm at any DPI, batch, crop, rotate — with a proper high-quality resampler. Free, in your browser.
Pixels, inches and DPI — the two-minute version
Digital images are pixels. Inches and centimetres only exist at print time, and DPI is just the exchange rate: pixels = inches × DPI. A 1200×1800 px photo is a razor-sharp 4×6" print at 300 DPI, an acceptable 8×12" at 150 DPI, and a poor poster at 50 DPI — same file, three descriptions. Two practical consequences:
- For screens (web, social, apps), ignore DPI entirely and think only in pixels.
- For print, work backwards from the physical size: the resizer lets you enter “10×15 cm at 300 DPI” directly and computes the pixels, and can write the DPI number into the file’s metadata since some print services read it.
Common targets
| Destination | Resize to |
|---|---|
| Full-width web hero | 1920 px wide (2560 for large screens) |
| Blog/article inline image | 1200–1600 px wide |
| Social media post | platform-exact — see the sizes cheat sheet |
| 4×6" print | 1200×1800 px (300 DPI) |
| A4 print | 2480×3508 px (300 DPI) |
| Email attachment | 1024–1600 px wide, then compress |
Sharpness killers to avoid
- Resizing in a hurry with the wrong tool. Cheap resizers use nearest-neighbour or basic bilinear filters that alias fine detail. A proper resampler (the resizer here uses a high-quality filter chain) preserves edges visibly better, especially for text and line art.
- Saving screenshots or text-heavy images as JPG. JPG smears sharp edges. Use PNG or WebP for anything with text; see the file-size guide for the format logic.
- Letting a platform do the resize. Uploading a 6000-px photo to a form that wants 800 px hands the job to the worst resizer in the chain. Do it yourself first.