Aspect Ratio Calculator & Image, Video and Screen Size Tools

A frame is a comparison of two numbers

An aspect ratio compares width to height and ignores size completely. That is the whole idea. A 1920 × 1080 video and a 3840 × 2160 video look identical in shape because both are 16:9, even though one contains four times as many pixels. When you scale a frame up or down and keep the ratio, nothing about the picture changes except how many pixels describe it.

Why ratios get simplified

Ratios describe proportions, not pixel counts. Any pair of numbers with the same quotient describes the same shape, so 1920:1080, 192:108 and 16:9 are three ways of writing one ratio. Dividing both numbers by their greatest common divisor gives the smallest whole-number form, which is the version people actually use. The calculator above shows the divisor it applied, so you can follow the reduction.

Ratio is not resolution

These two ideas are constantly confused. Resolution is the pixel count — how much detail the frame can hold. Ratio is the shape. Changing the ratio changes which parts of the frame exist; changing the resolution changes how much detail each part carries. That is why cropping a photo to a new ratio loses content but not sharpness, while stretching it to a new ratio keeps every pixel and ruins the picture.

When a ratio does not reduce to a common value

Not every frame is a standard shape. A 1366 × 768 laptop panel is sold as 16:9 but is really 683:384, about 0.05% wider than the standard. A 3440 × 1440 ultrawide monitor is called 21:9 but is actually 43:18. The calculator reports the closest common ratio together with how far away it is, so you can tell a true standard frame from a near miss.

To find the aspect ratio of any width and height, run the two numbers through the steps below. The calculator at the top of this page does the same reduction and shows the divisor it used.

The three-step method

1. Divide the width by the height to get the decimal ratio. For 1920 × 1080 that is 1.777…
2. Find the greatest common divisor of the two numbers. For 1920 and 1080 it is 120.
3. Divide both numbers by that divisor to get the smallest whole-number ratio: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9.

Worked example: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so 1920 × 1080 is 16:9 (120 is the greatest common divisor). Once you determine the aspect ratio this way, you can resize to it with the converter above.

The same calculation written out

gcd(1920, 1080) = 120
1920 / 120 = 16
1080 / 120 = 9
ratio = 16:9
decimal = 1920 / 1080 = 1.778

Going the other way: from a ratio to a size

When you know the ratio and one dimension, the missing side is a single division followed by a multiplication. For 16:9 at 1920 pixels wide: 1920 ÷ 16 = 120, then 120 × 9 = 1080. The same routine works for any ratio, including decimal ones — for 2.39:1 at 1920 wide, 1920 ÷ 2.39 = 803, so the anamorphic frame is 1920 × 803.

Why the calculator refuses decimals

Aspect ratios are built from whole pixels, because a screen cannot display half a pixel. If a width of 1920.5 were rounded silently to 1921, the reported ratio would be slightly wrong and the error would be invisible in the interface. Instead of quietly rounding, this calculator rejects decimal input and tells you why — so the ratio it reports is the true reduced form of what you typed.

Fitting a video to a platform

Every platform specifies a pixel size, not a vague shape. YouTube wants 1920 × 1080, Reels and Shorts want 1080 × 1920, and Instagram's feed portrait is 1080 × 1350. Enter the size you have and the target ratio you need, and the numbers tell you whether you are cropping away a quarter of the frame — or two thirds of it — before you sit down to edit.

Cropping a photo without guessing

A crop is capped by whichever side is shorter. From a 3000 × 2000 photo the largest square you can take is 2000 × 2000; anything larger is upscaled rather than genuinely recovered. Checking that ceiling first avoids the most common print and listing mistake: a square that looks sharp on screen and soft in the hand.

Setting a responsive element in CSS

A single aspect-ratio declaration keeps an embed, a card or a hero image the right shape at every width, and it removes the layout shift that happens when an image loads without reserved space. Copy CSS gives you the declaration already reduced to whole numbers.

Checking a monitor or laptop panel

Marketing labels are rounded. A 3440 × 1440 ultrawide is sold as 21:9 but reduces to 43:18, and a 1366 × 768 laptop sold as 16:9 is really 683:384. The calculator reports the exact reduction alongside the closest common ratio, so you know whether a wallpaper or a crop built on the round number will actually land flush.

Printing without an unexpected trim

Print sizes are ratios in inches. Standard photo prints are almost all 3:2, so a 4:3 or 16:9 file gets trimmed at the lab. Working out the crop beforehand — rather than discovering it on the receipt — is the difference between the frame you composed and the frame you get.

Add a free, live aspect ratio calculator to any page in one line of code - no account, no API key, no ads. Every embed credits the tool with a Powered by AspectCalc link, so your readers always know where it came from. See the full embedding guide for height and styling options.

Copy this snippet:

<div class="aspectcalc-embed" style="max-width:100%">
  <iframe id="aspectcalc-frame" src="https://aspectcalc.com/embed?h=640"
          width="100%" height="700" style="border:0;border-radius:12px"
          loading="lazy" title="AspectCalc aspect ratio calculator"></iframe>
  <p style="margin:8px 0 0;font:13px/1.4 system-ui,sans-serif;color:#64748b;text-align:center">Powered by <a href="https://aspectcalc.com/" style="color:#2563eb;text-decoration:none">AspectCalc</a> - free aspect ratio calculator</p>
</div>
<script>
  // Optional: grow the frame to the widget's real height.
  // Delete this whole block to keep a fixed-height frame instead.
  addEventListener('message', function (e) {
    if (e.origin !== 'https://aspectcalc.com') return;
    if (!e.data || e.data.type !== 'aspectcalc-height') return;
    var f = document.getElementById('aspectcalc-frame');
    if (f) f.style.height = e.data.height + 'px';
  });
</script>

Copy code

The frame starts at a fixed height, so your layout never jumps. Resize it with ?h= - for example https://aspectcalc.com/embed?h=520 - or keep the small script in the snippet and the frame will follow the widget's real height instead.