Last updated: October 2026
How to calculate aspect ratio
Short answer: find the greatest common divisor (GCD) of the width and height, then divide both numbers by it. 1920 × 1080 has a GCD of 120 → 1920÷120 : 1080÷120 = 16:9.
- Take your width and height. For example, a Full HD frame: 1920 × 1080.
- Find the GCD. The largest number that divides both evenly — for 1920 and 1080, it's 120.
- Divide both sides. 1920 ÷ 120 = 16, 1080 ÷ 120 = 9. Your ratio is 16:9.
- To resize: new height = new width × (9 ÷ 16). A 1280-wide version is 1280 × 9 ÷ 16 = 720 px tall.
GCD = greatest common divisor(width, height)
Aspect ratio = (width ÷ GCD) : (height ÷ GCD)
Decimal ratio = width ÷ height
Aspect ratio = (width ÷ GCD) : (height ÷ GCD)
Decimal ratio = width ÷ height
The decimal form is handy for comparing shapes: 16:9 ≈ 1.778, 4:3 ≈ 1.333, 1:1 = 1.0, 9:16 ≈ 0.563. Read the background on Wikipedia's aspect ratio (image) article.
16:9 aspect ratio calculator
Short answer: 16:9 means 16 units wide for every 9 tall — the widescreen standard for YouTube, HDTV and most monitors. Common 16:9 sizes: 1280 × 720 (720p), 1920 × 1080 (1080p), 2560 × 1440 (1440p), 3840 × 2160 (4K).
Pick the 16:9 preset in the “Resize to ratio” tab, enter any width, and the tool returns the matching height — for example 1280 → 720, 1920 → 1080, 3840 → 2160. Every one of those is the same shape, just more or fewer pixels: resolution changes detail, ratio changes shape.
9:16 ratio in pixels — vertical video sizes
Short answer: 9:16 is 16:9 turned on its side — the vertical shape of TikTok, Reels and Shorts. The standard full-size frame is 1080 × 1920; half-size is 720 × 1280.
Shooting or exporting vertical? Select the 9:16 preset and enter your known dimension. A 1080-wide clip needs 1920 px of height; if your canvas is only 1280 tall, the matching width is 720. Getting this right before export avoids the black bars and auto-cropping that platforms apply to wrongly-sized uploads.
Image aspect ratio calculator — photos and social posts
Short answer: most cameras shoot 3:2 (DSLR/mirrorless) or 4:3 (phones, compacts); social crops are usually 1:1 (1080 × 1080) or 4:5 (1080 × 1350). Enter your photo's dimensions above to confirm its ratio before you crop.
When a platform asks for a specific shape, don't guess — resize with the ratio locked. A 3:2 photo (6000 × 4000) cropped to Instagram's 4:5 portrait becomes 1080 × 1350 with no distortion, and after sizing, run it through our image compressor to hit the platform's file-size limit.
Common aspect ratios cheat sheet
Short answer: 16:9 for video and screens, 9:16 for vertical video, 1:1 and 4:5 for social feeds, 3:2 and 4:3 for photos, 21:9 for ultrawide.
| Ratio | Example size | Used for |
|---|---|---|
| 16:9 | 1920 × 1080 | YouTube, HDTV, presentations, 1080p/4K |
| 9:16 | 1080 × 1920 | TikTok, Reels, Shorts, Stories |
| 1:1 | 1080 × 1080 | Instagram feed squares |
| 4:5 | 1080 × 1350 | Instagram portrait posts |
| 4:3 | 1600 × 1200 | iPad screens, older cameras, classic TV |
| 3:2 | 6000 × 4000 | DSLR/mirrorless photos, 35mm film |
| 21:9 | 3440 × 1440 | Ultrawide monitors, cinematic |
Frequently asked questions
What is an aspect ratio calculator?
An aspect ratio calculator finds the proportional relationship between an image or video's width and height, written as W:H. Enter any dimensions — for example 1920 × 1080 — and it simplifies them to the smallest whole-number ratio, which is 16:9. It can also work in reverse: pick a ratio and one dimension, and it computes the matching dimension.
How do you calculate aspect ratio?
Find the greatest common divisor (GCD) of the width and height, then divide both by it. For 1920 × 1080, the GCD is 120, so 1920 ÷ 120 : 1080 ÷ 120 gives 16:9. To resize while keeping the ratio, use new height = new width × (ratio height ÷ ratio width).
What is the best aspect ratio calculator?
The best one gives you an instant answer with no signup, shows both the simplified ratio and the decimal, includes one-click presets for 16:9, 9:16, 4:3 and 1:1, and lets you resize to a new dimension — all of which the calculator on this page does, entirely in your browser.
What does 16×9 mean?
16×9 (written 16:9) means the image is 16 units wide for every 9 units tall — the widescreen shape used by HDTV, YouTube, and most monitors. Common 16:9 sizes include 1280 × 720 (720p), 1920 × 1080 (1080p) and 3840 × 2160 (4K).
What is a cross dimensions calculator?
A cross dimensions calculator — also called a proportional scaling calculator — takes one known dimension and a target ratio and computes the matching dimension, so the image keeps its shape. Use the “Resize to ratio” tab above: pick 16:9, enter a width of 1280, and it returns a height of 720.
What is an aspect ratio visualizer?
An aspect ratio visualizer draws the actual shape of a ratio so you can see it, not just read numbers. This page includes one: every calculation renders a live preview frame in the exact proportions of your ratio, which makes it easy to compare 16:9 against 9:16 or 1:1 at a glance.
What is the 4:5 pixel ratio?
The 4:5 ratio means 4 units wide for every 5 units tall — a portrait shape. Its most common pixel size is 1080 × 1350, the maximum size for Instagram portrait feed posts. Pick the 4:5 preset in the “Resize to ratio” tab to compute matching dimensions.
Is a tire aspect ratio calculator the same thing?
No — that's a different, automotive meaning. A tire's aspect ratio is the sidewall height expressed as a percentage of the tire's width (for example the “55” in 205/55R16). This page covers image and video aspect ratios only, not tire sizing.
Is my data private?
Completely. Every calculation runs locally in your browser with JavaScript — your dimensions are never sent to a server, stored, or tracked.