Aspect Ratio Calculator
Solve width or height from a ratio, simplify any resolution to its aspect ratio, and preview crop vs letterbox between ratios.
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Try FreeSolve a Dimension
Lock an aspect ratio, then type a width or a height — the other side is solved live.
Find the Ratio
Enter a pixel size to get its simplified aspect ratio, the nearest standard, and the decimal.
Crop & Letterbox Preview
Crop to fill
Source fills the target — overflow is cropped.
kept · cropped away
Letterbox / pillarbox (fit)
Whole source fits the target — bars fill the gaps.
video · bars
Common Resolutions
The standard delivery sizes for the two most common ratios — landscape 16:9 and vertical 9:16.
| Name | 16:9 (landscape) | 9:16 (vertical) |
|---|---|---|
| 720p — HD | 1280 × 720 | 720 × 1280 |
| 1080p — Full HD | 1920 × 1080 | 1080 × 1920 |
| 1440p — QHD | 2560 × 1440 | 1440 × 2560 |
| 4K — UHD | 3840 × 2160 | 2160 × 3840 |
Calculating, not resizing.
This page does the aspect-ratio math — dimensions, ratios and how a frame crops or letterboxes. To actually re-frame a video file for Instagram, TikTok or YouTube, you'll want a dedicated resizer (a social video resizer — coming soon). For the rest of the export math, see the Video Bitrate Calculator and the Video File Size Calculator, or add up edit timecodes with the Timecode Calculator.
About Aspect Ratio Calculator
What is an aspect ratio?
An aspect ratio is the proportion between a frame's width and its height, written as width:height (for example 16:9). It describes shape, not size: 1280×720, 1920×1080 and 3840×2160 are all 16:9 because each width divides to the same proportion as its height. Two resolutions with the same aspect ratio scale cleanly into each other; mismatched ratios need cropping or bars.
Common ratios and where they're used
| Ratio | Shape | Typical use |
|---|---|---|
| 16:9 | Landscape | YouTube, TV, most web video — the default widescreen frame |
| 9:16 | Vertical | Instagram Reels, TikTok, YouTube Shorts, Stories |
| 1:1 | Square | In-feed social posts |
| 4:5 | Tall portrait | Instagram feed video (more screen than 1:1) |
| 4:3 | Classic | Standard-definition and older broadcast footage |
| 2.39:1 | Anamorphic | Cinematic widescreen, the letterboxed film look |
How to compute a missing dimension
From a locked ratio A:B, the two sides are linked by simple proportion:
- Height from width:
height = width × B ÷ A - Width from height:
width = height × A ÷ B
For 16:9 at 1920px wide, the height is 1920 × 9 ÷ 16 = 1080. To find a ratio from pixels instead, divide both numbers by their greatest common divisor: 1920 and 1080 share a divisor of 120, which reduces to 16:9.
Crop vs letterbox vs pillarbox
When a source ratio doesn't match the target frame, you have two choices. Cropping scales the source to fill the frame and trims whatever spills over — going 16:9 to 9:16 keeps full height but loses about 68% of the width. Letterboxing (bars on the top and bottom) and pillarboxing (bars on the left and right) instead fit the whole source inside the frame and pad the gap, keeping every pixel of the original at the cost of empty bars. The preview on this page shows both for any pair of ratios.
Why even dimensions matter
Most delivery codecs — H.264 and H.265 among them — encode in blocks and require even pixel width and height (chroma subsampling samples colour in 2×2 groups). An odd dimension like 1080×607 will be rejected or silently padded by the encoder, so when a calculation lands on an odd or fractional number, round it to the nearest even value before you export.
How to use the Aspect Ratio Calculator
Lock an aspect ratio - 16:9, 9:16, 1:1, 4:5, 4:3, 21:9, 2.39:1 or a custom A:B.
Type a width or a height and the calculator solves the other side in whole pixels, flagging odd numbers an H.264 or H.265 encoder would reject.
Open the crop-versus-letterbox preview to see how one ratio sits inside another, then reframe the file itself with the Social Video Resizer.
Frequently Asked Questions
16:9 is the standard widescreen aspect ratio — 16 units of width for every 9 of height. In pixels the common 16:9 resolutions are 1280×720 (720p), 1920×1080 (1080p), 2560×1440 (1440p) and 3840×2160 (4K). It's the default frame for YouTube, television and most web video.
Divide the width and height by their greatest common divisor (GCD). For 1920×1080 the GCD is 120, so it reduces to 16:9. To go the other way and find a missing side from a known ratio A:B, use height = width × B ÷ A or width = height × A ÷ B. Both modes are built into the calculator above.
9:16 is the vertical (portrait) ratio used for Reels, TikTok and Shorts. The standard sizes are 720×1280, 1080×1920, 1440×2560 and 2160×3840 — the same numbers as the 16:9 resolutions with width and height swapped. 1080×1920 is the usual delivery size.
Cropping fills the new frame completely and trims the overflow, so you lose part of the picture but keep the frame full. Letterboxing (bars top and bottom) or pillarboxing (bars left and right) keeps the entire picture and pads the empty space with bars instead. Use the preview above to see how much each costs for any pair of ratios.
H.264 and H.265 require even width and height because colour is sampled in 2×2 blocks. If a ratio calculation lands on an odd number like 607 or a fraction like 1080.5, round it to the nearest even value before exporting — the calculator flags this for you automatically.
This calculator works out the numbers — the target dimensions and how the frame crops or letterboxes — but it doesn't process video files. To actually re-frame and re-export a clip for a different platform you need a video resizer (a dedicated social video resizer is on the way); paste the dimensions you solve here into your editor's sequence or export settings.
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