Aspect ratio calculator

How to use the aspect ratio calculator

1. Pick a mode. Find the ratio tells you the ratio of a size you already have. Resize gives you a new size that keeps a ratio.
2. Find the ratio. Type the width and height in pixels. You get the simplified ratio, the decimal ratio and the nearest common ratio.
3. Resize. Tap a ratio such as 16:9 or 4:3, or type your own. Then type a width or a height. The calculator fills in the other side, rounded to a whole pixel. To use it as a 16:9 aspect ratio calculator, tap 16:9 and type the width.

The preview box shows the shape, so you can see at a glance whether it is wide, tall or square.

New to the idea? Read the guide: what aspect ratio is and which sizes to use on a website.

How an aspect ratio is worked out

An aspect ratio is the width compared with the height. To simplify it, divide both numbers by their greatest common divisor (GCD), the largest number that divides both exactly.

Aspect ratio = (Width ÷ GCD) : (Height ÷ GCD)

Worked example: 1920 x 1080

• The greatest common divisor of 1920 and 1080 is 120.
• 1920 ÷ 120 = 16.
• 1080 ÷ 120 = 9.
• The aspect ratio is 16:9. As a decimal, 16 ÷ 9 = 1.778.

To resize, turn the formula around.

Height = Width × Ratio height ÷ Ratio width

A 16:9 video that is 1280 pixels wide is 1280 × 9 ÷ 16 = 720 pixels high. If you know the height instead, the width is Height × Ratio width ÷ Ratio height.

Not every size simplifies neatly. 1366 x 768, a common laptop screen, works out to 683:384. That is very close to 16:9 but not exact, so the calculator shows 16:9 as the nearest common ratio.

Common aspect ratios in pixels

Every size in a row has the same shape. Only the amount of detail changes.

Ratio	Decimal	Common sizes in pixels	Where you see it
16:9	1.778	1280 x 720, 1920 x 1080, 3840 x 2160	TVs, monitors, online video
16:10	1.6	1280 x 800, 1920 x 1200, 2560 x 1600	Laptops
4:3	1.333	1024 x 768, 1600 x 1200, 2048 x 1536	Tablets, slides, older screens
3:2	1.5	1080 x 720, 2160 x 1440, 3000 x 2000	Camera photos
1:1	1	1080 x 1080	Square posts, profile pictures
4:5	0.8	1080 x 1350	Portrait social posts
9:16	0.563	720 x 1280, 1080 x 1920	Vertical phone video
21:9	2.333	2520 x 1080, 3360 x 1440	Ultrawide monitors

Ultrawide monitors sold as 21:9 are usually 2560 x 1080 or 3440 x 1440. Those are 64:27 and 43:18, a little wider than a true 21:9.

Practical notes

• Image aspect ratio on a website. Add the width and height to each image tag. The browser then knows the shape before the file loads and keeps the space free, so the page does not jump.
• Screen aspect ratio is not resolution. The ratio is the shape. The resolution is the number of pixels. A 1280 x 720 screen and a 3840 x 2160 screen are both 16:9.
• Resize or crop. Keeping the ratio scales a picture with no distortion. Changing the ratio means cropping part of it or adding bars.
• Rounding. Some sizes cannot hit a ratio with whole pixels. The calculator rounds to the nearest pixel and tells you when it does. For an exact 16:9 size, use a width that divides by 16.

Need the picture in another format at its new size? Use the SVG to PNG converter or the PNG to WebP converter. More tools like this are on the website tools page.

How this calculator was checked

Built by Rasel Hakkani, WordPress developer at Swift Web Dev. The results were checked against hand-worked answers, including 1920 x 1080, 1366 x 768, portrait sizes and resizes that do not land on a whole pixel. Every size in the table was reduced by hand to confirm its ratio.

Last checked: October 2026. Found a wrong answer? Tell us and we will fix it.