Aspect Ratio Calculator
Work out the missing dimension that keeps an image or video at the same shape — and name the ratio.
An aspect ratio is width divided by height, reduced to its simplest whole-number form.
How the aspect ratio calculator works
An aspect ratio is width divided by height, reduced to its simplest whole-number form. 1920 × 1080 divides by 120 to give 16:9.
Resizing without distortion means holding that ratio: fix one dimension and the other follows. Give this page a source size and one target dimension and it fills in the rest.
The common ratios are worth recognizing. 16:9 is broadcast and YouTube; 9:16 is the vertical of TikTok and Reels; 4:3 is older monitors and iPads; 3:2 is most mirrorless cameras; 21:9 is ultrawide; 1:1 is a square post.
Formula: new height = new width × (original height / original width)
Worked examples
| Inputs | New size | Note |
|---|---|---|
| 1920 × 1080 scaled to 1280 wide | 1280 × 720 px | 1280 × 720, still 16:9 |
| A 4:3 photo to 800 wide | 800 × 600 px | 800 × 600 |
| Fitting a height instead | 711 × 400 px | 711 × 400 |
FAQFrequently asked questions
What is an aspect ratio?
Width divided by height, reduced to whole numbers. 1920 × 1080 is 16:9.
How do I resize without distortion?
Change one dimension and let the other follow the ratio. Setting both independently stretches the image.
What ratio is 1920 × 1080?
16:9 — the standard for HD video and most monitors.
What is the ratio for TikTok and Reels?
9:16 vertical, typically 1080 × 1920.
Why do cinema ratios not reduce neatly?
Because 1.85:1 and 2.39:1 were defined as decimals from film formats, not as small whole-number ratios.
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.