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The Calculator Corner

Aspect Ratio Calculator

Find a ratio from pixel dimensions, or resize without distortion.

Original1920 × 1080New1280 × 720

Common ratios (20)

Original

Resize to

Aspect ratio

16:9

New size
1280 × 720 px
As a decimal
1.778

What an aspect ratio actually is

An aspect ratio describes a frame's shape, independent of its size. It's the width divided by the height, written as two whole numbers separated by a colon. A 16:9 frame is sixteen units wide for every nine tall — whether those units are pixels on a phone or metres on a cinema screen. That's why 1280 × 720 and 3840 × 2160 look identical in shape despite one having nine times the pixels: both reduce to 16:9.

The practical consequence is that ratio, not resolution, decides whether an image fits. Put a 4:3 photo into a 16:9 slot and something has to give: black bars down the sides, a crop off the top and bottom, or a stretch that makes everyone look wider than they are.

Using this aspect ratio calculator

Enter the width and height you're starting from. The ratio appears immediately, along with the decimal form — useful when you're comparing two frames that are close but not identical. The preview above the fields draws both frames to scale, so an ultrawide monitor next to a square social post looks the way it actually would.

To resize, edit one of the two "New" fields and watch the other one follow. Type a new width and the height fills itself in; type a new height instead and the width is recalculated. Whichever box you touched last is the one being obeyed, and the other is the answer — which is the whole trick to resizing an image without distorting it.

Calculating aspect ratio from pixels

The arithmetic is a single proportion. Divide width by height for the decimal, then reduce the two numbers by their greatest common divisor for the familiar colon form. 1920 and 1080 share a divisor of 120, which is how 1920:1080 becomes 16:9. 800 × 600 shares 200 and becomes 4:3.

Reduction is also the fastest way to catch a ratio that's been mislabelled. Screens sold as "16:10" are 8:5 once reduced — the same shape under a friendlier-sounding name. This calculator always reduces fully, so two frames with the same shape always produce the same answer no matter how the spec sheet phrased it.

Ratios worth knowing

16:9 is video and nearly every screen. 4:3 is older monitors, tablets and a lot of camera sensors. 3:2 comes from 35 mm film and is still what most mirrorless cameras shoot. 1:1 and 4:5 are square and portrait social posts, 9:16 is the full-screen vertical format used by stories and short video. Cinema mostly lives at 1.85:1 or 2.39:1, which are wide enough that the decimal form is how they're written.

The "Common ratios" panel under the fields holds twenty standard frame sizes — broadcast, cinema, desktop and social. Clicking one fills the original dimensions for you, which is quicker and less error-prone than typing four digits from memory.

Where ratios go wrong

Two failures account for most distorted images. The first is entering both new dimensions by hand: unless they happen to land on the same proportion, something stretches. The second is rounding at every step of a chain of resizes, where each half-pixel compounds — resize once from the original rather than repeatedly from the last version.

If what you actually need is proportional scaling rather than frame shape — reducing a set of numbers by a fixed factor — the percentage calculator handles that side of the arithmetic.

FAQ

How do you calculate aspect ratio?
Divide the width by the height, then reduce it to its smallest whole numbers. A 1920 × 1080 image divides to 1.778, and 1920:1080 reduces to 16:9 — both describe the same shape. To resize without distortion you keep that number fixed: new height = original height × (new width ÷ original width). Resizing 1920 × 1080 down to 1280 wide gives 1080 × (1280 ÷ 1920) = 720, so the new frame is 1280 × 720.
What is 1920 × 1080 as an aspect ratio?
16:9. It's the standard for Full HD video, almost every television and monitor, and YouTube. The same 16:9 shape covers 1280 × 720, 2560 × 1440, 3840 × 2160 and 7680 × 4320 — they differ in resolution, not in proportion, which is why footage cuts between them without black bars.
Why does this show 8:5 instead of 16:10?
Because 8:5 is the fully reduced form, and they're the same ratio — 16:10 just hasn't been divided through by 2. A 2560 × 1600 laptop screen is described as 16:10 by manufacturers because it reads as a sibling of 16:9, but reduce the numbers properly and you get 8:5. This calculator always shows the smallest whole numbers, so you can tell at a glance when two differently-worded ratios are actually identical.
Why do some ratios show as a decimal like 2.39:1?
Because their reduced form is useless. Cinema's Scope format is 2048 × 858, which reduces exactly to 1024:429 — technically correct and completely unreadable. Whenever the reduced form needs numbers that big, the calculator falls back to the decimal notation the film industry uses anyway, so Scope shows as 2.39:1 and Flat (1998 × 1080) as 1.85:1 rather than 37:20. Portrait frames are inverted for the same reason: A4 paper at 300 dpi is 2480 × 3508, shown as 1:1.41 rather than 0.71:1.
How do I resize an image without stretching it?
Change one dimension and let the calculator supply the other. Enter your original width and height, then edit either the new width or the new height — the field you didn't touch updates itself to the matching value. The preview draws both frames to scale, so you can see the shape hasn't changed. Typing both numbers from your own head is exactly how images end up squashed.
Can I resize to a target height instead of a width?
Yes — just type into the New height field. Whichever of the two you edited last is treated as your requirement, and the other is recalculated from it, so editing the height solves for the width. That's what you want when the constraint is a fixed row height or a banner slot rather than a column width.
Are the results always whole pixels?
Yes — results are rounded to the nearest whole pixel, because a fractional pixel isn't a thing an image can have. That rounding can shift the true ratio by a hair on awkward numbers: 1000 × 333 resized to 500 wide gives 167 rather than 166.5. For screen work the difference is invisible; if you need the exact proportion, the decimal figure in the results is unrounded to three places.

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