Image Resize Calculator
Scale an image by a percentage or to a target size, and estimate the file size that results.
Resizing scales both dimensions by the same factor, so the pixel count — and roughly the file size — changes with the square of that factor.
How the image resize calculator works
Resizing scales both dimensions by the same factor, so the pixel count — and roughly the file size — changes with the square of that factor. Halving the width and height leaves a quarter of the pixels, which is why dropping an image to 50% cuts the file to about a quarter, not a half.
The file-size estimate assumes JPEG at the quality you pick. Real files vary a great deal with content: a photo of foliage compresses far worse than a plain sky, so treat the figure as an order-of-magnitude guide.
Enlarging past 100% cannot add detail — the pixels are interpolated, so the image gets bigger and softer.
Formula: new pixels = original pixels × scale²; JPEG bytes ≈ pixels × bits-per-pixel / 8
Worked examples
| Inputs | New dimensions | Note |
|---|---|---|
| A 12 MP photo at 50% | 2000 × 1500 px | 2000 × 1500 — a quarter of the pixels |
| Down to 25% | 1000 × 750 px | 1000 × 750 |
| Enlarging | 1600 × 1200 px | 1600 × 1200, but no new detail |
FAQFrequently asked questions
How do I resize an image without distorting it?
Scale both dimensions by the same percentage. Changing one alone stretches the picture.
Why does halving the size quarter the file?
Because both dimensions halve, so the pixel count — and roughly the file size — falls by a factor of four.
Can I enlarge an image without losing quality?
No. Enlarging interpolates between existing pixels; it cannot recover detail that was never captured.
How accurate is the file-size estimate?
It is a guide. A photo of foliage can be several times larger than a photo of a plain sky at the same dimensions and quality.
What JPEG quality should I use?
Around 85 for photos you care about — the step down to 70 saves a lot of bytes with little visible loss, and below 50 artefacts become obvious.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- NIST — Digital Identity Guidelines (SP 800-63) — US federal authentication standard
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.