Aspect Ratio Calculator
Type a width and height to get the ratio, like 16:9, and the matching height for a new width, as you type. Advanced adds resizing by percent, fit or fill inside a box, print size at a DPI and screen size from the diagonal.
New size, same ratio
Fit inside a box
A screen, a frame or a post size. Leave blank to skip.
Print size
300 is the usual for photo prints, 150 for posters seen from further away. It also links pixels to inches when you switch units.
Screen size
Uses the ratio of your width and height. With a size in pixels you also get the sharpness (pixels per inch).
How your aspect ratio is worked out
Divide the width and height by the biggest number that goes into both. Keep that ratio to resize without stretching.
- 1
Width and height
1920 × 1080 px
- 2
Find the GCD
GCD = 120
- 3
Divide both by it
1920 ÷ 120 = 16
1080 ÷ 120 = 9
= 16:9 (1.78:1) - 4
New size, same ratio
1280 × 9 ÷ 16
= 720
1280 × 720
Read more: the formula, a worked example, fit and fill, common ratios and sizes
An aspect ratio is the shape of a rectangle: its width compared with its height. 1920 × 1080, 1280 × 720 and 3840 × 2160 are different sizes but the same shape, 16:9. Keep the ratio when you resize and nothing gets squashed or stretched.
The formula
ratio = (width ÷ GCD) : (height ÷ GCD), where GCD is the greatest common divisor of width and height
ratio as a decimal = width ÷ height, written as “that : 1”
new height = new width × height ÷ width
new width = new height × width ÷ height
fit in a box: scale = the smaller of (box width ÷ width) and (box height ÷ height); fill: the bigger one
print size in inches = pixels ÷ DPI · pixels needed = inches × DPI · megapixels = width × height ÷ 1,000,000
screen width = diagonal × ratio width ÷ √(ratio width² + ratio height²) · PPI = √(px width² + px height²) ÷ diagonal in inches
Worked example
1920 × 1080 pixels. The greatest number that divides both is 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9. As a decimal, 1920 ÷ 1080 = 1.777…, which rounds to 1.78:1. It has 1920 × 1080 = 2,073,600 pixels, which is 2.07 megapixels.
To resize to 1280 wide and keep the shape: 1280 × 1080 ÷ 1920 = 720, so the new size is 1280 × 720. That is 1280 ÷ 1920 = 66.67% of the original.
Fit or fill: a 16:9 video in a 1080 × 1080 square post
| How | Working | What you get |
|---|---|---|
| Fit | scale = smaller of 1080 ÷ 1920 = 0.5625 and 1080 ÷ 1080 = 1, so 0.5625. 1920 × 0.5625 = 1080, 1080 × 0.5625 = 607.5 | 1080 × 607.5 picture with a letterbox: (1080 − 607.5) ÷ 2 = 236.25 px bars above and below. 43.75% of the square is bars. |
| Fill | scale = bigger of 0.5625 and 1, so 1. The picture stays 1920 × 1080 | 1920 − 1080 = 840 px cropped from the width, 420 px off each side. 43.75% of the picture is lost. |
Common aspect ratios
| Ratio | Decimal | Used for |
|---|---|---|
| 16:9 | 1.78:1 | HD and 4K TVs, YouTube, most monitors |
| 4:3 | 1.33:1 | old TVs, iPads, many compact cameras |
| 21:9 | 2.33:1 | ultrawide monitors and phones |
| 3:2 | 1.50:1 | DSLR and mirrorless photos, 6 × 4 in prints |
| 1:1 | 1.00:1 | square posts and profile pictures |
| 9:16 | 0.56:1 | phone video, Reels, TikTok, Stories, Shorts |
| 4:5 | 0.80:1 | portrait posts on Instagram and Facebook |
| 2.39:1 | 2.39:1 | cinema widescreen (scope) |
| 1.85:1 | 1.85:1 | cinema flat widescreen |
| 32:9 | 3.56:1 | super-ultrawide monitors |
| 16:10 | 1.60:1 | many laptops and MacBooks |
| 5:4 | 1.25:1 | older office monitors, 10 × 8 in prints |
| 2:1 | 2.00:1 | some phones and streaming shows |
| 3:4 | 0.75:1 | portrait photos from phones and tablets |
| 2:3 | 0.67:1 | portrait camera photos, 4 × 6 in prints |
Screens sold as “21:9” are usually 2560 × 1080 (exactly 64:27, 2.37:1) or 3440 × 1440 (43:18, 2.39:1). DCI 4K cinema, 4096 × 2160, is 256:135, about 1.90:1, a little wider than 4K UHD TVs at 16:9.
Common sizes
| Name | Pixels | Ratio |
|---|---|---|
| HD 720p · YouTube thumbnail | 1280 × 720 | 16:9 |
| Full HD 1080p | 1920 × 1080 | 16:9 |
| QHD 1440p | 2560 × 1440 | 16:9 |
| 4K UHD | 3840 × 2160 | 16:9 |
| DCI 4K (cinema) | 4096 × 2160 | 256:135 (1.90:1) |
| 8K UHD | 7680 × 4320 | 16:9 |
| Instagram square post | 1080 × 1080 | 1:1 |
| Instagram portrait post | 1080 × 1350 | 4:5 |
| Story, Reel, TikTok, Shorts | 1080 × 1920 | 9:16 |
| A4 at 300 DPI (210 × 297 mm) | 2480 × 3508 | about 1:1.414 |
| US Letter at 300 DPI (8.5 × 11 in) | 2550 × 3300 | 17:22 |
| 6 × 4 in photo at 300 DPI | 1800 × 1200 | 3:2 |
Print size and DPI
Pixels have no size until you print or show them. Divide by the dots per inch: 3000 × 2000 pixels at 300 DPI print at 3000 ÷ 300 = 10 by 2000 ÷ 300 = 6.67 inches (25.4 × 16.93 cm). The other way, A4 is 8.27 × 11.69 inches, so at 300 DPI it needs 8.27 × 300 = 2480 by 11.69 × 300 = 3508 pixels.
Screen size from the diagonal
A 27 inch 16:9 monitor: √(16² + 9²) = 18.36, so the width is 27 × 16 ÷ 18.36 = 23.53 in and the height 27 × 9 ÷ 18.36 = 13.24 in. At 2560 × 1440 the diagonal has √(2560² + 1440²) = 2937.2 pixels, and 2937.2 ÷ 27 = 108.8 pixels per inch.
Video sizes follow the ITU and DCI standards; social sizes are the ones the apps recommend and can change. Paper sizes: A4 from ISO 216, US Letter from ANSI. Real screens can differ slightly from the diagonal sum because of rounded corners. Checked 13 October 2026.
Common questions
What is the aspect ratio of 1920 × 1080?
16:9. The greatest number that divides both 1920 and 1080 is 120, and 1920 ÷ 120 = 16, 1080 ÷ 120 = 9. As a decimal that is 1.78:1. HD, Full HD, 4K UHD and 8K UHD are all 16:9.
How do I work out the height for a new width?
New height = new width × old height ÷ old width. To resize 1920 × 1080 to 1280 wide: 1280 × 1080 ÷ 1920 = 720, so the new size is 1280 × 720. Use the same idea the other way to find a width from a height.
What does letterbox and pillarbox mean?
When a picture is fitted inside a screen of a different shape, the leftover space shows as bars. Bars above and below are a letterbox (a wide film on a 16:9 TV); bars at the sides are a pillarbox (a 4:3 video on a 16:9 screen). Filling the screen instead crops the edges off.
Is 21:9 really 21:9?
Usually not exactly. Ultrawide monitors sold as 21:9 are 2560 × 1080 (64:27, about 2.37:1) or 3440 × 1440 (43:18, about 2.39:1). True 21:9 is 2.33:1. The calculator shows the exact ratio and the name it is sold under.
How many pixels do I need to print A4 at 300 DPI?
A4 is 210 × 297 mm, which is 8.27 × 11.69 inches. At 300 dots per inch that is 2480 × 3508 pixels, about 8.7 megapixels. US Letter (8.5 × 11 in) at 300 DPI is 2550 × 3300 pixels.
How do I find a screen’s width and height from its size?
Screens are measured corner to corner. Width = diagonal × ratio width ÷ √(ratio width² + ratio height²). A 27 inch 16:9 monitor is 27 × 16 ÷ 18.36 = 23.53 inches wide and 13.24 inches high.
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