Aspect Ratio Calculator

An aspect ratio is the proportion between an image's width and its height, written as W:H. A 1920 x 1080 screen has a greatest common divisor of 120, so it reduces to 16:9; a 16:9 image that is 1600 px wide is therefore 1600 × 9 ÷ 16 = 900 px tall. This calculator finds the ratio of any dimensions and solves the missing width or height for any target ratio.

It is the visual cousin of our Ratio Calculator. Use that page when you are comparing two abstract quantities, such as a recipe or a mixture; use this one when the two numbers are a width and a height and you need pixels, prints or screens to line up.

How the calculator works

Two operations cover almost every aspect ratio question. The first reduces a pair of dimensions to their simplest form by dividing both by their greatest common divisor:

The second solves a proportion. When you know the target ratio R_w:R_h and one dimension, the other follows by cross-multiplication:

The calculator also expresses the ratio as a decimal (W ÷ H) and as height-as-a-percent-of-width (H ÷ W × 100). For 16:9 those are 1.7778 and 56.25%; for 4:3 they are 1.3333 and 75.00%. Decimals make ratios easy to compare: the bigger the number, the wider the frame.

Worked example 1: what ratio is 4032 x 3024?

A typical 12-megapixel phone photo measures 4032 x 3024 pixels. Finding the GCD with Euclid's method: 4032 ÷ 3024 leaves remainder 1008, and 3024 ÷ 1008 leaves remainder 0, so the GCD is 1008. Dividing both sides gives 4032 ÷ 1008 = 4 and 3024 ÷ 1008 = 3, so the photo is 4:3. As a decimal, 4032 ÷ 3024 = 1.3333, and the frame holds 4032 × 3024 = 12.19 million pixels. Because 4:3 is much taller than a 16:9 screen, showing this photo full-width on a Full HD monitor requires either black bars or cropping 25% of its height (see the cropping table below).

Worked example 2: a 9:16 vertical video from a known height

Suppose you are exporting a vertical clip 1920 px tall and need the width for a 9:16 frame. Using the width formula, width = 1920 × 9 ÷ 16 = 1080 px, so the export size is 1080 x 1920. The ratio is 0.5625 as a decimal, meaning the width is 56.25% of the height. Had you needed a 21:9 frame 2560 px wide instead, the height would be 2560 × 9 ÷ 21 = 1097.14 px, which the calculator rounds to 1097 px and flags because pixels cannot be split; the rounded frame reduces to 2560:1097, off from true 21:9 by a negligible fraction of a percent.

Height for common ratios by width

Every value below is width × ratio height ÷ ratio width. Where the exact answer is not a whole number, the decimal is shown so you can see how much rounding a given width requires. Widths divisible by 16 give clean 16:9 heights; widths divisible by 21 give clean 21:9 heights.

The 1:1 column is left out because it is trivial: a square is exactly as tall as it is wide, so 1,080 px wide means 1,080 px tall.

Common resolutions and the ratio they reduce to

The table lists familiar screen, camera and print sizes with the GCD used to reduce them. Note the "almost" cases: 1366 x 768 and the ultrawide panels are marketed under a round ratio but do not reduce to it.

How to use this aspect ratio calculator

1. Pick a mode. "Find the ratio" takes a width and height and reduces them. "Resize to a ratio" takes a target ratio and one known dimension and returns the other.
2. Find mode: type the pixel width and height, or tap one of the quick sizes (1920 x 1080, 4032 x 3024, 6000 x 4000 and so on). Read the simplified W:H, the decimal, the GCD and the closest named ratio. If the size matches a preset exactly, a table of common resolutions in that ratio appears; if not, a comparison table shows what height each standard ratio would need at your width.
3. Resize mode: choose 16:9, 4:3, 21:9, 1:1, 9:16 or 3:2, or select "Custom" and type any two numbers such as 16 and 10. Say whether you know the width or the height, enter it, and read the missing dimension. A note appears whenever the exact answer is not a whole pixel.
4. Apply it in your editor. The calculator gives numbers, not files. Enter the resulting width and height in the crop or export dialog of your photo or video software with "constrain proportions" turned on.

Who this calculator is for

• Video creators exporting one edit for a 16:9 YouTube upload and a 9:16 vertical cut, and needing both frame sizes to be exact.
• Web designers and developers sizing hero images, thumbnails and CSS aspect-ratio boxes so that nothing stretches or leaves gaps.
• Photographers deciding how much of a 3:2 frame survives a 4 x 6, 5 x 7 or 8 x 10 print order.
• Gamers and PC builders checking whether a monitor is really 16:9, 16:10 or "21:9", and what resolution to run a game at.
• Anyone buying a TV, frame or projector screen who wants to know how a given format will fit.

Key terms explained

• Aspect ratio: width divided by height, written W:H. It describes shape only, never size.
• Resolution: the number of pixels across and down, such as 2560 x 1440. Many resolutions share one ratio.
• Greatest common divisor (GCD): the largest whole number that divides both dimensions. Dividing by it produces the simplest ratio. For 1920 and 1080 it is 120.
• Landscape, portrait, square: a decimal above 1 is landscape (wider than tall), below 1 is portrait, exactly 1 is square.
• Letterboxing and pillarboxing: the black bars added above and below (letterbox) or left and right (pillarbox) when content is shown on a screen of a different ratio without cropping.
• Megapixels: width × height ÷ 1,000,000. A 3840 x 2160 frame is 8.29 MP; 6000 x 4000 is 24.00 MP.
• Pixel density (PPI): pixels per inch of physical size. It links pixels to print inches but does not change the aspect ratio.

Cropping between ratios: how much you lose

Changing the ratio of an existing image always means cropping (or adding bars). The loss is the difference between the original dimension and what the new ratio allows, keeping the other dimension fixed. Each row below keeps the full width (or, for the print row, the full height) and trims the rest.

The last row explains why landscape video looks so cramped as a square post: almost half the width is gone. Shooting with the final ratio in mind, or leaving generous margins, avoids the problem.

Fitting without cropping: bars and scaling

If you would rather keep every pixel, the content is scaled to fit and the leftover space becomes bars. A 4:3 program on a 1920 x 1080 screen is scaled to 1440 px wide (1080 × 4 ÷ 3), leaving 240 px pillarbox bars on each side and using 75% of the screen width. A 2.39:1 widescreen film on the same screen fills 1920 × 1 ÷ 2.39 = 803.3 px of height, leaving letterbox bars of roughly 138 px top and bottom. And a 1920 x 1080 landscape clip dropped into a 1080 x 1920 vertical frame shrinks by a factor of 0.5625 to 1080 x 607.5 px, with 656.25 px of empty space above and below, which is why vertical platforms push creators to reframe rather than pad.

What changes the result the most

• Whether the dimensions share a large factor. 1920 x 1080 reduces cleanly because both are multiples of 120. 1366 x 768 shares only a factor of 2, so its "simplest" form is the unwieldy 683:384. Odd sizes from hand-cropping often behave this way; the calculator's closest-ratio line tells you what you were probably aiming for.
• Which dimension you hold fixed. Solving for height from a width and solving for width from a height are different questions. Cropping a 3:2 photo to 4:5 while keeping the height cuts 16.67% of the width; keeping the width instead would require adding height, which is impossible without padding.
• Rounding to whole pixels. Whenever width × R_h is not divisible by R_w, the exact answer has a fraction. 1000 px wide at 16:9 is 562.5 px tall; you must choose 562 or 563. Picking widths that are multiples of the ratio's width term (16, 4, 3, 21) removes the issue.
• Marketing names versus real ratios. "21:9" panels are 64:27 or 43:18; "16:9" 1366 x 768 is 683:384. When exactness matters, calculate from the pixel counts, not the label.
• Orientation. 9:16 and 16:9 have identical decimals inverted (0.5625 and 1.7778). Swapping width and height flips the orientation but not the amount of image; the calculator reports both.

Tips for cleaner results

• When you have a choice, start from a width that is a multiple of the ratio's first number. For 16:9, widths of 1280, 1600, 1920, 2560 and 3840 all give whole-pixel heights (720, 900, 1080, 1440, 2160).
• Export video at an even width and height. Many encoders require both dimensions to be divisible by 2, so a 16:9 clip 1001 px wide (563.06 px tall) is a poor choice on two counts.
• For prints, first match the ratio, then worry about pixel density. An 8 x 10 needs a 4:5 crop; at 300 pixels per inch that crop should be at least 2400 x 3000 px, which a 5000 x 4000 crop from a 24 MP camera comfortably exceeds.
• On the web, set aspect-ratio: 16 / 9 (or the ratio you calculated) on image and video containers so the layout reserves the right space before the file loads.
• Keep the decimal handy. Comparing 1.7778 to 1.6000 tells you instantly that a 16:9 video on a 16:10 screen will show thin bars, without drawing anything.

Limitations and assumptions

• The calculator works in whole pixels. Fractional results are rounded to the nearest pixel and flagged; it never rounds silently.
• It assumes square pixels. A handful of older video formats use non-square pixels, where the stored resolution and the displayed ratio differ.
• It does not know about pixel density, physical size or file size. A 4:5 crop can be printed at 8 x 10 inches or 16 x 20 inches; the ratio is identical, the PPI is not.
• It does not crop or resize your image. It tells you the numbers to enter in your editor.
• "Closest standard ratio" compares against the common named ratios only (16:9, 4:3, 21:9, 1:1, 9:16, 3:2, 16:10, 5:4, 4:5, 2:3, 3:4, 1.85:1 and 2.39:1). Unusual formats may be nearest to one of these without being intended as it.

How it compares to related calculators

This page answers "what shape is this image, and what size keeps that shape?" For neighboring questions, a sister tool fits better:

• To simplify, scale or solve a ratio that is not a width and a height, such as a mixture or a recipe, use the Ratio Calculator.
• To work with the same relationship as a fraction (9/16 = 0.5625), use the Fraction Calculator.
• To express a crop as a percent of the original or work out a percent change in size, use the Percentage Calculator.
• To convert print sizes between inches and centimeters before matching a ratio, use the Unit Converter.

In short: reach for the Ratio Calculator when the two numbers are abstract quantities, and for this Aspect Ratio Calculator when they are pixels, inches or screen dimensions and you need the missing side.

Sources

• The reduction uses Euclid's algorithm for the greatest common divisor and the missing dimension comes from cross-multiplication. Both are elementary arithmetic and need no external source.
• Resolution figures (1280 x 720, 1920 x 1080, 3840 x 2160, 4032 x 3024, 6000 x 4000 and so on) are the pixel counts of the formats themselves; the ratios and percentages on this page are computed from those counts, not quoted from a third party.