Height for a 16:9 width
The everyday video case, in one keystroke.
Input
Ratio 16:9 · Target width 1920Output
Height 1080 — the preview shows the widescreen shape with both dimensions labelledAspect Ratio Calculator
Enter one dimension and get the other, locked to 16:9, 9:16, 4:3, 1:1, 21:9, 3:2, 4:5, or any custom ratio, with a live shape preview.
- Free public tool
- No sign-up for this tool
- Processing clearly labeled
- Instant results
Content last reviewed
Edit either width or height. The other value will update automatically to maintain the 16:9 ratio.
1920px
1080px
16:9Quick Start
Pick the ratio
Choose a preset like 16:9 or 1:1, or enter a custom ratio width and height.
Enter one dimension
Type the width or the height — the other updates instantly to match the ratio.
Check the preview
The live shape preview confirms the proportions before you use the numbers.
Examples
Width from a height, portrait ratio
Working backwards from a known height in a vertical format.
Input
Ratio 4:5 · Target height 1350Output
Width 1080 — the Instagram portrait pairAbout the Aspect Ratio Calculator
"The video is 16:9 and needs to be 1280 wide — how tall is that?" is a thirty-second mental-math stumble that this calculator answers instantly, in both directions. Fix an aspect ratio, type either dimension, and the matching value appears, rounded to whole pixels and previewed as a live shape so the proportions are visible, not just numeric.
The preset list covers the ratios that actually come up: 16:9 for widescreen video and YouTube, 9:16 for vertical TikTok/Reels/Shorts, 4:3 for standard displays and older footage, 1:1 for square posts, 21:9 for ultrawide and cinematic frames, 3:2 for classic photography, and 4:5 for Instagram portrait. Anything else — an odd banner slot, a custom canvas — is a Custom entry away: type any ratio width and height and the same bidirectional math applies.
It is deliberately a calculator, not an editor: it manipulates numbers, never files, which makes it the planning companion to the hands-on tools. Work out that your 16:9 export at 1080 tall means 1920 wide here, then do the actual pixel work in the Image Resizer, frame platform crops in the Social Media Image Resizer, or take the numbers straight into your video editor's project settings.
How to Use Aspect Ratio Calculator
Under Define Aspect Ratio, pick a preset from the dropdown — 16:9, 9:16, 4:3, 1:1, 21:9, 3:2, or 4:5 — or select Custom and enter your own ratio width and height.
In Calculate Dimensions, type your known value into Target Width or Target Height.
The other field updates immediately, rounded to whole pixels, keeping the exact ratio. Editing either field recalculates the other, in whichever direction you work.
Glance at the visual preview — the box redraws at the true proportions with the dimensions labelled — and use the numbers wherever they are needed.
Key Features
Bidirectional calculation
Edit width to get height or height to get width — both directions stay locked to the ratio.
Seven common presets
16:9, 9:16, 4:3, 1:1, 21:9, 3:2, and 4:5, each labelled with its typical use.
Fully custom ratios
Enter any ratio width and height for non-standard slots and canvases.
Whole-pixel rounding
Results round to integers, since fractional pixels do not exist in exports.
Live shape preview
A proportionally accurate box redraws as you type, with the current dimensions labelled.
When to Use Aspect Ratio Calculator
Video export settings
Find the missing dimension for a 16:9 or 21:9 timeline at your target width or height.
Design canvases
Size banners, artboards, and layout slots that must hold exact proportions.
Pre-resize planning
Compute the distortion-free target before entering numbers into the Image Resizer.
Responsive layout math
Derive the pixel pairs behind CSS aspect-ratio boxes and embedded player sizing.
How It Works
The math is one proportion applied both ways: height = width ÷ (ratioW ÷ ratioH) and width = height × (ratioW ÷ ratioH), with results rounded to whole pixels. Choosing a preset sets the ratio pair and recalculates the height from the current width; editing the custom ratio fields does the same and flips the selector to Custom. The preview scales the true proportions into a fixed-size box, wide ratios filling horizontally and tall ratios vertically, so the shape you see is the shape you will get.
Supported Formats and Options
Options
Ratio preset
16:9, 9:16, 4:3, 1:1, 21:9, 3:2, 4:5, or Custom.
Custom ratio width and height
Free numeric fields defining any proportion; editing them switches the preset to Custom.
Target width / target height
Enter either; the other recalculates to hold the ratio.
Common Errors and Troubleshooting
Common errors
The other field changed when you didn't expect it
That is the tool working — the two dimension fields are linked through the ratio, so editing one always recalculates the other. To change the shape itself, change the ratio, not the dimensions.
Result is off by one pixel from a spec
Rounding to whole pixels can differ by one from a platform's published pair when the ratio doesn't divide evenly. Use the platform's exact published dimensions when they exist; the calculator is for when they don't.
Confusing ratio with resolution
1920×1080 and 1280×720 are different resolutions with the same 16:9 ratio. The ratio fixes the shape; the dimension you type picks the size.
Troubleshooting guide
Getting from ratio to usable numbers
- Know the slot, not the ratio: divide the slot's width by its height — 1200 ÷ 628 ≈ 1.91 — and enter that as a custom ratio (191:100 works) to generate other sizes for the same shape.
- Need several sizes of one shape: keep the ratio fixed and type each target width in turn; every output pair shares identical proportions.
- Cropping rather than scaling: a ratio change means cropping, not resizing — take the numbers to the Social Media Image Resizer or Quick Image Editor, which cut to shape instead of stretching.
- Very tall or wide previews look small: extreme ratios (a 10:1 banner) render as a thin sliver at preview scale — the numbers remain exact even when the preview is necessarily tiny.
Limitations and Important Notes
It calculates numbers only — no files are read, resized, or cropped, and it does not know any platform's current published specs beyond the standard ratios (the Social Media Image Resizer carries the named presets). Results round to whole pixels, which can differ by a pixel from spec pairs whose ratio does not divide evenly. There is no copy button; the values are read from the fields.
Privacy and Data Processing
Everything is arithmetic in your browser — no images, no uploads, nothing stored. The values you type exist only on the page.
Tips and Best Practices
Practical tips
Round to whole pixels — which the tool already does — since fractional pixels blur edges.
Lock the ratio first, then derive every size you need from it for a consistent set.
Use custom ratios for odd slots: divide the slot's width by its height to find the ratio.
Remember ratio ≠ resolution — pick the shape here, the size in your export settings.
When the shape must change, plan a crop (not a stretch) and hand off to the cropping tools.
Best practices
Ratio-first sizing
Decide the shape before any size. Whether the frame is 16:9, 4:5, or a custom banner proportion, fixing it first means every derived size — thumbnail, full-size, retina — shares the exact geometry, and nothing gets stretched to fit later.
Generate size families in one sitting: with the ratio locked, type each target width in turn and record the pairs. A components spec that says "all cards are 3:2 at 300, 600, and 900 wide" is this calculator used properly.
And route shape changes through cropping. When an asset must move from 3:2 to 1:1, the calculator tells you the target numbers, but the pixels should be cut, not squashed — that is the Quick Image Editor's or Social Media Image Resizer's job, with this tool as the planner.
Technical Details
Pure client-side arithmetic: the linked fields apply height = width ÷ (ratioW/ratioH) and its inverse with Math.round to integers; preset selection re-derives height from the current width, and custom ratio edits flip the selector to Custom. The preview box scales the ratio into a 300-pixel maximum extent, filling the constrained axis. No files, storage, or network are involved.
Comparison
The preset ratios and where they live
| Ratio | Orientation | Typical home |
|---|---|---|
| 16:9 | Wide | YouTube, HD video, slides |
| 9:16 | Tall | TikTok, Reels, Shorts, Stories |
| 4:3 | Wide | Standard displays, older footage |
| 1:1 | Square | Instagram grid, avatars |
| 21:9 | Ultra-wide | Cinematic frames, ultrawide monitors |
| 3:2 | Wide | Classic photography, many cameras |
| 4:5 | Tall | Instagram portrait posts |
Who Is This For?
Video editors setting export dimensions, designers sizing canvases and banner slots, developers deriving the pixel pairs behind responsive embeds, and anyone mid-task who needs "the other number" for a fixed shape without doing division in their head.
Frequently Asked Questions
What is an aspect ratio?
The proportional relationship between width and height, written as width:height — 16:9 means 16 units across for every 9 down. Two images can share a ratio at completely different sizes: 1920×1080 and 1280×720 are both 16:9.
How do I keep an image's proportions when resizing?
Fix the ratio here, enter your one known dimension, and use the calculated pair in the Image Resizer. Matching proportions is exactly what prevents stretching or squashing.
What ratio do vertical social videos use?
9:16 — the full-screen vertical format of TikTok, Instagram Reels and Stories, and YouTube Shorts. Horizontal video and standard YouTube use 16:9. Both are presets.
Can I use a ratio that isn't in the list?
Yes — choose Custom and enter any ratio width and height. For an odd slot, divide its width by its height to find the ratio (a 1200×628 card is about 191:100) and the calculator handles the rest.
Why did the height change when I edited the width?
The fields are linked through the ratio by design — that is the calculation. Editing either dimension recalculates the other so the pair always matches the chosen shape; change the ratio itself to change the shape.
Does this resize my actual image?
No — it is a pure calculator. Take the numbers it gives you to the Image Resizer for scaling, or to the cropping tools when the shape needs to change.