How to Calculate an Image’s Aspect Ratio
Updated
To calculate an image ratio, divide the width and the height by the largest number that fits into both. For 1920 × 1080 that number is 120, which gives 16:9.
How do I work out the ratio step by step?
You only need the width and height in pixels, from the file’s info panel:
- Write the size as width × height, for example 1920 × 1080.
- Find the greatest common divisor, the biggest number that divides both with nothing left over. Here it is 120.
- Divide both sides by it: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9.
- Write the answer as 16:9.
For a decimal ratio, divide the width by the height instead. 1920 ÷ 1080 = 1.78, so the ratio is 1.78:1.
What are the ratios of common image sizes?
The table works each size through the same steps, with the divisor in the middle column.
Ultrawide 3440 × 1440 reduces to 43:18, which is close to 2.39:1. It is sold as 21:9, a rounded marketing name.
How do I find the height for a given ratio?
Height = width × the second number ÷ the first number. For a 16:9 image 1280 px wide, that is 1280 × 9 ÷ 16 = 720 px.
How do I crop an image to a set ratio?
Most photo editors have a crop tool with a ratio setting. The steps are much the same everywhere:
- Open the image and choose the crop tool.
- Pick the ratio from the list, such as 16:9 or 4:5, or type your own.
- Drag the box over the part you want to keep, then apply the crop.
Cropping throws away the edges, so keep a copy of the original.
Is there a faster way?
Yes. Type the width and height into our aspect ratio calculator and it does every step for you. It also finds a missing width or height.
Which aspect ratios are most common?
A handful of shapes cover almost every screen and image you will meet. Each one has its usual home:
- 16:9: TVs, most monitors, laptops and online video.
- 16:10: many laptops and some office monitors, a little taller than 16:9.
- 4:3: older monitors, many tablets and phone camera photos.
- 3:2: photos from most full-frame and APS-C cameras.
- 21:9: ultrawide monitors, sold under that rounded name.
- 1:1: square images for profile pictures and posts.
- 9:16: upright video made for phones.
Compare common screen sizes in each shape in our screen resolution chart.
What is the difference between 16:9 and 16:10?
At the same width, 16:10 is taller. A 1920 × 1200 screen has 120 more rows of pixels than 1920 × 1080, which is 11% more room for text and toolbars.
That is why many work laptops use 16:10. Video still fills a 16:9 screen better, so 16:10 shows thin bars above and below a film.
Does aspect ratio change how big a screen is?
Yes. Screens are sold by the diagonal, and the shape decides how that diagonal splits into width and height. A 27 inch 16:9 screen is 23.5 in (59.8 cm)59.8 cm (23.5 in) wide, while a 27 inch 4:3 screen is only 21.6 in (54.9 cm)54.9 cm (21.6 in) wide.
The 4:3 screen also has more area, about 350 square inches against 312. Our screen size calculator works out width, height and area for any diagonal and shape.
Ultrawides show the same effect. A 34 inch 21:9 monitor is 31.4 in (79.7 cm)79.7 cm (31.4 in) wide but only 13.1 in (33.3 cm)33.3 cm (13.1 in) tall.
Why do black bars appear around videos?
Bars appear when a video’s ratio does not match the screen. The player shrinks the video to fit and fills the rest with black.
- Bars above and below: the video is wider than the screen, such as a 2.39:1 film on a 16:9 TV.
- Bars at the sides: the video is narrower, such as a 4:3 show or upright phone video.
A 2.39:1 film leaves about 26% of a 16:9 screen black. On a 65 inch TV, that is a bar about 4.1 in (10.5 cm)10.5 cm (4.1 in) tall at the top and bottom.
How do I keep the ratio when I resize an image?
Change one side and let the editor work out the other. In most editors, a lock or chain icon next to the size boxes keeps the ratio fixed.
To do it by hand, use new height = new width × old height ÷ old width. A 4032 × 3024 photo resized to 1600 px wide becomes 1600 × 3024 ÷ 4032 = 1200 px tall.
Our resolution scale calculator does the same sum for any size, and shows the result at common widths.
What aspect ratio is my screen?
Our screen size detector reads your screen’s resolution and works out its ratio in your browser. Most monitors and TVs are 16:9, so that is the safe guess for a desktop screen.
Phones are taller and narrower than any monitor. See our iPhone screen sizes for each model’s exact shape and resolution.
What aspect ratio are photo prints?
Print sizes are named in inches, and each has its own ratio. That is why a phone photo often needs cropping before printing:
- 4 × 6 in: 3:2, the same shape as most camera photos.
- 5 × 7 in: 5:7, a little squarer than 3:2, so the ends of the photo are trimmed.
- 8 × 10 in: 4:5, much squarer, so even more is trimmed from the ends.
A 4:3 phone photo printed at 4 × 6 loses a strip from the top or bottom.
How do I find the aspect ratio of a screen in inches?
The same method works with measured sizes. Divide the width by the height and match the decimal:
- Measure the visible screen width and height, without the frame.
- Divide width by height. For example, 23.5 ÷ 13.2 = 1.78.
- Match the decimal: 1.78 is 16:9, 1.6 is 16:10, 1.33 is 4:3 and about 2.4 is 21:9.
Our guide on how to measure on screen and the monitor size checker can help with the measuring.
What aspect ratio do projectors and cinemas use?
Home projectors and screens use 16:9, the same as TVs. Many films are shot wider, at about 2.39:1, which leaves bars at the top and bottom.
Some home cinema fans buy a 2.35:1 screen to match. Our guide to projector screen sizes shows each shape’s width and height.
What aspect ratio should a presentation be?
Use 16:9 for anything shown on a TV, monitor or modern projector. PowerPoint and Google Slides both start new decks at 16:9.
Pick 4:3 only for an older projector. A 16:9 slide on a 4:3 screen shrinks to fit, leaving bars above and below.
Questions
Can two different sizes have the same aspect ratio?
Yes. 1280 × 720 and 3840 × 2160 are both 16:9, because both reduce to the same pair.
What aspect ratio is a phone screen?
Recent phones are much taller than 16:9, at about 19.5:9 to 20:9. Divide the height by the width to check yours.
What aspect ratio is A4 paper?
A4 is 210 × 297 mm, a ratio of about 1.41:1. Every A size has this same shape.
What aspect ratio is a 4 × 6 photo?
It is 3:2. The greatest common divisor is 2, and 4 ÷ 2 : 6 ÷ 2 gives 2:3, which is 3:2 turned sideways.
Is aspect ratio width by height or height by width?
Width comes first. A 16:9 image is 16 units wide for every 9 units tall.
Does resizing an image change its aspect ratio?
Not if you keep the lock or chain icon on, which scales both sides together. Cropping or stretching one side does change it.
What ratio is 1920 × 1200?
It is 16:10. The greatest common divisor is 120, and 1920 ÷ 120 = 16 while 1200 ÷ 120 = 10.
Is 9:16 the same as 16:9?
It is the same shape turned on its side. 9:16 is tall, like a phone held upright, and 16:9 is wide, like a TV.
What ratio is 4K?
Consumer 4K, 3840 × 2160, is 16:9. Cinema 4K, 4096 × 2160, is wider, at about 1.9:1.
Why does my ratio come out as odd numbers?
Some sizes do not reduce to a neat pair. Compare the decimal form instead, such as 1.78:1 for 16:9.
How we measure
Ratio = width ÷ gcd : height ÷ gcd, where gcd is the greatest common divisor found with Euclid’s method. The decimal form is the long side divided by the short side, to two places.