Free Aspect Ratio Calculator
Work out any aspect ratio instantly with our 100% free aspect ratio calculator. Enter a size to get its true ratio — 1920x1080 is 16:9, not 1.78 — then resize to a new width or height without distortion in seconds, with presets for screen, camera, social and paper. No signup, no downloads needed. Trusted by 60,000+ artists worldwide.
The size you have
The size you want
Common ratios
The figures
- New height
- 675
- Resized to
- 1200 × 675
- Decimal ratio
- 1.78
- Orientation
- Landscape
The arithmetic runs in this page. Nothing is sent anywhere.
Both directions of the same question
Give a size and a new width and it returns the height that does not distort; give a size alone and it returns the ratio, reduced by the greatest common divisor, so 1600 by 1000 reports 8:5 rather than a decimal.
2 controls, not a fixed result
Set width and height. Every change redraws the sheet, in this page's own document.
Part of the calculators set
The set also holds mural grid calculator and canvas size calculator, all of them free and all of them working in the browser.
The ratio, drawn
Both sizes are drawn to scale sharing a corner, with a dashed ray through each far corner: any rectangle whose corner sits on that line has the same proportions, so the drawing itself is the proof that the resize did not distort.
- 100% free
- No signup
- No watermark
- Nothing is uploaded
Enter a size and get its true reduced ratio — 1920 by 1080 is 16:9, not 1.78. Enter one side of a new size and get the other. Presets for screen, camera, social and paper formats. Those ratios are what several of the 82 composition overlays are built on — each root rectangle and the phi grid is defined by one.
- True reduced ratio
- 12 presets
- Either direction
- Nothing uploaded
What is an aspect ratio calculator?
An aspect ratio calculator reduces a width and a height to the simplest whole numbers that describe their proportion, and works out the missing side when you change one of them. The reduction matters: 1600 by 1000 is 8:5, and a calculator that reports 1.6 has told you something true and much less useful.
How to calculate an aspect ratio
Two numbers in, and the ratio, the simplified form and the resized dimensions out. The arithmetic that sits behind every crop, done once instead of in your head.
Enter the size you have
An aspect ratio calculator starts from two numbers: type the width and height in any unit — pixels, inches, centimetres. A ratio has no units, so it does not matter which, as long as both are the same. The canvas size calculator turns a ratio into a stretcher size, and the proportion calculator scales one surface to another.
JPG · PNG · GIF · WEBP
Read the reduced ratio
The result is reduced by the greatest common divisor, so it comes back as 16:9 or 8:5 rather than as a decimal. The decimal is given underneath for when that is what you need.
Rectangle outline · Reciprocals
Give one side of the new size
Type the new width and the height follows, or switch the direction and give the height instead. Either way the proportion is preserved exactly.
PNG · JPG · PDF · SVG · up to 600 DPI
Three steps, about a minute. No signup, no upload.
What the Aspect Ratio Calculator does
It reduces properly
An aspect ratio calculator reduces by the greatest common divisor, so 1600 by 1000 comes back as 8:5. A decimal of 1.6 is the same fact in a form you cannot type into a crop tool.
Both directions
Sometimes you know the width you can print and sometimes the height the wall allows. It solves for whichever one you did not type.
Presets that are real formats
Screen, camera, social and paper — each stored as a ratio rather than a pixel size, so it stays correct at any output resolution.
A figure you can see
The ratio is drawn as a rectangle at the correct proportions. A number is easy to mistype; a shape that suddenly looks wrong is not.
It answers as you type
No submit, no reload. Trying five canvas sizes takes about ten seconds.
Nothing leaves the page
Arithmetic in a browser. No account, no logging, nothing recorded.
Aspect ratio calculator examples: four ratios, drawn
Aspect ratio calculator vs a generic calculator site vs dividing it yourself
| Option | Reduces properly | Solves the other side | Format presets | Cost |
|---|---|---|---|---|
| Grid Maker Prothis tool | Yesgreatest common divisor | Either direction | Screen, camera, social, paper | Free, no account |
| A generic calculator site | Sometimes | Usually | Rarely | Free with ads |
| Dividing it yourself | Only if you reduce | Yes | No | Free |
| A design tool's crop panel | Shows the ratio it offers | Within that tool | Its own list | Subscription |
Who an aspect ratio calculator is for: the people deciding a shape before a size
How an aspect ratio calculator works — Why the reduced ratio is the useful answer
Every aspect ratio has a decimal form, and almost nothing you want to do with one accepts a decimal. The reduction is not cosmetic — it is what makes the number usable.
An aspect ratio is the relationship between width and height, and it survives scaling: 1920 by 1080, 1280 by 720 and 640 by 360 are all the same shape. Reducing by the greatest common divisor is what recovers the name of that shape. All three of those reduce to 16:9, and 16:9 is what a camera menu, a crop tool and a video encoder all expect you to type.
Why the reduced ratio beats the decimal
The decimal is the same fact and a worse handle on it. 1.777… does not tell you at a glance that the shape is the standard widescreen one, and 1.6 could be 8:5 or 16:10 depending on how it was rounded — which are the same shape, but only one of those is what the device actually reports. Reduction removes that ambiguity by producing the smallest whole numbers that are exactly right.
The reduction also exposes a distinction people frequently miss, which is that a ratio and a size are different kinds of thing. 4:5 is a shape. 1080 by 1350 is a size that happens to have that shape. Instagram's feed limit is expressed as the second, and treating it as the first is how a design ends up correctly proportioned and too small.
Stock surfaces, and paper
Where this bites hardest for anyone drawing or painting is stock surfaces. Canvases and frames come in sizes chosen by manufacturers, not by ratio, and the popular ones are not consistent with each other: 8×10 is 4:5, 11×14 is 11:14, 16×20 is 4:5 again, 18×24 is 3:4. A photograph shot at 3:2 fits none of them. That is not a defect in the photograph — it is the reason cropping exists — but it is much better decided deliberately at the start than discovered when the drawing is half done.
Paper is more coherent and worth knowing about for the same reason. The A series is built on a ratio of 1:√2, chosen precisely so that halving the long side reproduces the same shape: A4 folded is exactly A5. That is why an A-series document scales between sizes without a margin changing shape, and why US Letter — 8.5 by 11, which reduces to 17:22 — does not.
Film and video ratios
Film and video carry their own set, and the numbers are historical rather than principled. 4:3 is the Academy ratio inherited from 35mm silent film; 16:9 was chosen in the 1980s as a compromise that could letterbox both 4:3 and the wider cinema formats with the least waste; 2.39:1 is modern anamorphic scope. Knowing that they are conventions rather than derivations is useful, because it means there is no arithmetic that will tell you which one to shoot in.
The practical rule that comes out of all this is short: decide the ratio before the size, because the ratio is the thing the composition lives in and the size is only how large it is printed. This calculator gives you the first and then does the second, which is the order the work actually happens in.
The two ratios that come from geometry
Two ratios worth knowing separately are the ones that come from geometry rather than from convention. 1:1.414 is the A-series ratio and it is 1:root 2 exactly, which is what gives it the halving property. 1:1.618 is the golden ratio, and unlike the A series it has no self-similar folding property of that kind — what it has is that removing a square from a golden rectangle leaves a smaller golden rectangle, which is a different and more often misdescribed trick. Both turn up constantly in composition writing, and they are not interchangeable.
There is a common confusion between aspect ratio and orientation that is worth naming, because it produces real mistakes. 3:2 and 2:3 are the SAME proportion turned ninety degrees, and most tools treat them as different ratios because the order of the numbers encodes which side is which. That is the correct behaviour — a portrait canvas and a landscape canvas are not interchangeable — but it means comparing two ratios requires checking the orientation as well as the numbers. The orientation is reported here alongside the ratio for exactly that reason.
Resolution, cropping, and things that are not rectangles
For anyone working toward print, the last step after the ratio is resolution, and it is a separate calculation that people often merge into this one. A ratio has no resolution: 3:2 describes a shape at any pixel count. To go from a shape to a printable file you multiply by the DPI you intend — a 3:2 image at 12 by 8 inches and 300 DPI is 3600 by 2400 pixels. Deciding the shape first and the pixels second keeps those two decisions from contaminating each other, which is why this tool answers only the first.
A final practical note about cropping. When a reference does not match the surface, there are only three honest options and it is worth choosing between them deliberately: crop the reference to the surface's ratio and lose part of the image; letterbox it and accept a margin; or change the surface. Stretching is a fourth option and it is never the right one for representational work, because the human eye is extremely sensitive to distortion in faces and much less sensitive to a tighter crop.
One last case that catches people out is the ratio of a thing that is not rectangular. A circular crop, a rounded card, an app icon with a squircle mask — all of them still sit inside a bounding rectangle, and it is that rectangle's ratio the tools ask for. The visible shape is a mask applied afterwards. Designing to the mask and then discovering the bounding box is a different proportion is one of the more annoying ways to lose an afternoon, and checking the ratio of the box first avoids it entirely.
Where an aspect ratio calculator gets used
Every commission starts with a reference at one ratio and a canvas the client already bought at another. Getting the reduced ratio of both, side by side, makes the crop conversation concrete instead of vague.
The one that catches people is stock canvas sizes. Nothing an ordinary camera produces fits 11×14, and it is far better to know that before the drawing than after.
For print I need the ratio, not a pixel size — the pixel size follows from the DPI. A calculator that hands back a decimal makes me do the reduction myself.
Video is the case where getting it wrong is expensive, because the fix is a re-export rather than a re-crop. Deciding the delivery ratio before the edit starts — not after the grade — is the whole discipline.
Aspect ratio calculator: frequently asked questions
The geometry
What is an aspect ratio?
An aspect ratio is the proportion between a rectangle's width and its height, written as two numbers. It describes shape rather than size: 1920 by 1080 and 640 by 360 are different sizes and the same 16:9 shape.
What is 1920 by 1080 as a ratio?
16:9. It is the standard widescreen shape for televisions, monitors and most video, and it reduces from 1920 by 1080, 1280 by 720 and 3840 by 2160 alike.
Which aspect ratio should I use for Instagram?
The feed accepts 1:1 and 4:5, and 4:5 occupies the most vertical space in a scrolling feed. Stories and Reels are 9:16. Those are shapes; the pixel sizes that carry them change as the platform updates, which is why the ratio is the durable number.
Why do standard canvas sizes not match my photos?
Because canvas and frame sizes were chosen by manufacturers rather than derived from a ratio, and the common ones are inconsistent: 8×10 and 16×20 are 4:5, 11×14 is 11:14, 18×24 is 3:4. A 3:2 photograph fits none of them exactly, so something has to be cropped or a margin left.
Does the unit matter?
No. A ratio is a relationship between two numbers, so pixels, inches and centimetres all give the same answer as long as both measurements use the same one.
Is 16:10 the same as 8:5?
Yes. 16:10 reduces by 2 to 8:5, and both describe the same shape. Device manufacturers usually quote 16:10 because it reads as a sibling of 16:9; a calculator that reduces properly will report 8:5.
Using it
How do I calculate an aspect ratio?
Divide both numbers by their greatest common divisor. For 1920 and 1080 that divisor is 120, which gives 16:9. Dividing width by height instead gives the decimal form, 1.78, which is the same fact in a form most tools will not accept.
How do I resize an image without distorting it?
Change one dimension and derive the other from the ratio rather than choosing it. If the original is 3:2 and the new width is 1200, the height must be 800. Setting both independently makes the width and height scale by different amounts, which stretches the picture.
How do I use the overlay alongside the numbers?
Set the ratio, then look at the rectangle drawn on your image. The numbers tell you the proportion and the rectangle tells you what it costs — how much of the picture falls outside it, and off which edge. Those are different questions and the second one usually decides.
Should I turn the thirds on while checking a crop?
It helps for a crop you intend to keep. Seeing where the thirds land inside the new rectangle tells you whether your subject is still on a division after cropping, which is the thing that quietly stops being true when you change the ratio.
Export and print
What ratio is A4 paper?
1:√2, which is 1:1.414. The root-2 rectangle overlay is that proportion drawn, and the dynamic symmetry overlays hold the rest of the root rectangles. The A series is built on it so that halving the long side gives the same shape again — A4 folded in half is exactly A5 — which is why A-series documents scale between sizes without margins changing proportion.
How do I convert a ratio into pixels for print?
Multiply the shape by the resolution you intend. A 3:2 image printed 12 by 8 inches at 300 DPI needs 3600 by 2400 pixels. The ratio fixes the shape and the DPI fixes how many pixels carry it, which are two separate decisions worth keeping separate.
Choosing a grid
What is the difference between 3:2 and 2:3?
They are the same proportion in different orientations — 3:2 is landscape, 2:3 is portrait. The order of the numbers records which side is the width, so the two are not interchangeable when you are ordering a canvas or setting up a crop.
Why not use a generic ratio calculator?
Because a generic one gives you a decimal. 1600 by 1000 is 8:5, and a tool that reports 1.6 has answered a different question — you cannot look up 1.6 in a list of standard formats, and you cannot tell at a glance that it is the same shape as 16:10.
Is a design tool's crop panel not enough?
It is, for cropping. This is for the arithmetic around it — what the missing dimension is, whether two sizes are the same shape, what a ratio becomes in pixels at a print resolution. Those come up before you open the image.
Practical matters
Do my numbers get sent anywhere?
No. This is arithmetic running in your own browser. Nothing is submitted or logged, and the page keeps working with the network disconnected once it has loaded.
Is it free?
Yes, with no account and no usage limit. The core tools here are free permanently; the paid product is a separate augmented-reality tracing app.
Which ratio should I use for social platforms?
Check the platform rather than trusting any list, including this one — the accepted ratios change without notice. What does not change is the arithmetic: pick the ratio the platform states, and use this to work out the pixel dimensions that satisfy it at your resolution.
Can I use it on a phone?
Yes. It is entirely arithmetic and a small overlay, so it works as well on a phone as anywhere — and checking whether a shot will survive a 4:5 crop is a question that comes up on a phone more than on a desktop.
Open the tool Aspect ratio calculator
Shape first, size second
The true reduced ratio, and the dimension that keeps it. No signup, nothing uploaded.
Back to the generator →