Cropping fills the frame
The picture reaches every edge and whatever does not fit is cut away. A 1920 by 1080 master cropped to 9:16 keeps a strip 608 px wide, so two thirds of the picture is gone and anything framed near an edge goes with it.
Free calculator, no account
Aspect ratio calculator
Fill in the missing side of a frame, reduce any pixel size to its simplest ratio, and see which pixels a ratio change would throw away before you commit to it. Everything runs in this browser.
Nothing is uploaded. The arithmetic happens on this page.
The calculator
Solve it, then see what it costs
Pick a target, either one of the 7 presets or your own pair of numbers. The calculator then completes the frame from whichever side you type, reduces a size you already have to its lowest ratio, and shows a crop and a pad of the same frame side by side with the pixel count for every edge. That last part is the one worth reading before you export.
1. Choose a target ratio
Start from a preset or type your own pair. Decimals are fine: 2.39 and 1 is a valid ratio.
16:9 · 1.778 across for every 1 down
2. Fill in the missing side
Type a width and read the height, or type a height and read the width. Whichever one you type, the other stays locked to the ratio above.
1920 × 1080 px at 16:9.
3. See what the ratio change costs
Enter the size you are starting from. The left card crops it to the target ratio and the right card pads it instead, both with the pixel count for every edge.
Source is 16:9 · about 16:9
Crop to fit
- Kept
- 1920 × 1080
- Cut off the sides
- 0 px + 0 px
- Cut off top and bottom
- 0 px + 0 px
- Picture lost
- 0%
Pad to fit
- Delivered frame
- 1920 × 1080
- Bars left and right
- 0 px + 0 px
- Bars top and bottom
- 0 px + 0 px
- Frame that is bar
- 0%
When the pixels to remove do not divide in two, the odd one goes to the right or the bottom, which is what most crop tools do.
Cheat sheet
Aspect ratio chart
The 13 ratios you will actually meet, tallest first, each with a real frame delivered at that shape. Every figure is printed in the page itself, so it reads fine without JavaScript.
| Ratio | Decimal | Example frame | Where it turns up |
|---|---|---|---|
| 9:16Vertical | 0.563 | 1080 × 1920 | Shorts, Reels, TikTok and anything shot to be held upright. The tallest ratio in common use. |
| 2:3Portrait photo | 0.667 | 1200 × 1800 | A 35mm still turned upright, which is most cameras in portrait orientation. |
| 3:4Tall photo | 0.75 | 1080 × 1440 | Micro Four Thirds and phone cameras held upright, and a common generation preset. |
| 4:5Portrait post | 0.8 | 1080 × 1350 | The tallest a still image goes in most feeds before the feed crops it. |
| 1:1Square | 1 | 1080 × 1080 | Cover art, profile images, and posts that must not favour either orientation. |
| 4:3Classic | 1.333 | 1440 × 1080 | Television before widescreen, tablets, projected slides and a lot of archive footage. |
| 3:2Photo | 1.5 | 3000 × 2000 | A 35mm still on its side. The default frame of nearly every stills camera. |
| 16:10Computer wide | 1.6 | 1920 × 1200 | Laptop and monitor panels, so also most screen recordings. |
| 16:9Widescreen | 1.778 | 1920 × 1080 | HD and 4K video, YouTube, thumbnails and nearly every television made since 2005. |
| 1.85:1Flat | 1.85 | 1998 × 1080 | The narrower of the two standard cinema projections. |
| 2:1Univisium | 2 | 2048 × 1024 | A compromise between television and cinema, used by some streaming productions. |
| 64:27Ultrawide | 2.37 | 2560 × 1080 | Ultrawide monitors. Sold as 21:9, but a 2560 by 1080 panel is 64:27. |
| 2.39:1Scope | 2.39 | 2048 × 858 | Anamorphic cinema, and the frame most trailers are graded in. |
Two rows are rounded by convention rather than exactly. Scope is written 2.39:1, but the projected frame is 2.3869:1, and panels sold as 21:9 are really 64:27, or 2.37:1. The calculator uses the honest number in both cases.
The arithmetic
How an aspect ratio is worked out
An aspect ratio is one number: width divided by height. 16:9 is 1.778, 9:16 is 0.5625, and a square is 1. It says nothing about size, which is why 1280 by 720 and 3840 by 2160 are both 16:9. Everything else here is that division used in one of three directions.
To fill in a missing side, multiply the side you have by the ratio the right way round. Height is width times H divided by W, so a 16:9 frame 1600 px wide is 900 px tall. Width is height times W divided by H. The calculator floors the answer at one pixel, because a frame with a zero side is not a frame.
To turn a pixel size into a ratio, divide both sides by their greatest common divisor. 1920 and 1080 both divide by 120, which leaves 16:9. The method only helps when the numbers are friendly, though: a 1920 by 1004 crop reduces to 480:251, which tells you nothing. So the calculator also names the closest standard ratio, about 1.85:1 in that case, and prints the decimal.
Pixels are whole numbers, so a ratio that does not divide evenly has to be rounded and the result sits a fraction of a percent off. Round once at the end rather than at every step, because rounding twice compounds the error. And when the frame is going into a video encoder, round both sides down to an even number: H.264 stores colour at half resolution on each axis, so an odd side has no whole colour sample and most encoders reject the file.
Crop or pad
What a ratio change actually costs
There are only two honest ways to move a finished frame from one ratio to another, and both take something. Most calculators stop at the arithmetic and leave you to find out which one hurts less after the export.
Padding keeps everything
Every pixel survives at full size and bars fill the difference. Nothing is lost, but a 16:9 clip padded into a 9:16 frame is picture across a third of the height and bar across the rest, which viewers read as a re-upload.
Reframing beats both
If the ratio is settled before the frame exists, neither cost applies. That is the whole argument for choosing the shape first, because a crop is a decision made afterwards with less picture than you started with.
One practical rule falls out of those numbers: a 16:9 frame that might later become 9:16 has to hold its subject inside the middle third of the width, because that is all a vertical crop keeps. Check it with your own dimensions before you shoot or generate, not after.
Before you generate
Pick the ratio first, not after
PrismPoster asks which frame you want before it makes an image or a clip, so the picture is composed for that frame instead of being cut down to it later. The numbers above are the reason it works that way.
- The frame is a setting on the generation itself, not something applied to the result afterwards.
- If the exact ratio you need is not one of the presets, make the nearest one and trim it in the timeline editor. The crop card says what that costs before you commit.
- A new account comes with 50 starter credits, granted once. This calculator uses none of them and never asks you to sign in.
PrismPoster makes and edits media. It does not post or schedule anything to a social account, so the platform names on this page are only a description of where a frame usually ends up.
See what the studio makesQuestions
Aspect ratios, answered
What is an aspect ratio?
The proportion between the width of a frame and its height, written as two numbers with a colon between them. 16:9 means sixteen units across for every nine down. It describes shape, not size, so 1280 by 720 and 3840 by 2160 are both 16:9.
How do I work out the missing width or height?
Multiply the side you have by the ratio in the right direction: height is width times H divided by W, and width is height times W divided by H. A 16:9 frame 1600 px wide is therefore 900 px tall. The calculator does it as you type.
What aspect ratio should a YouTube video be?
16:9, usually at 1920 by 1080. Thumbnails are 16:9 as well, at 1280 by 720, and Shorts are 9:16 at 1080 by 1920. All three are presets above, so you can see what a 16:9 master loses on the way to a Short.
Should I crop the frame or add bars?
Crop when the subject sits near the middle and the edges are expendable. Pad when losing any part of the picture would be worse than the bars, which is usually true of text, product shots and anything signed in a corner. The two cards above give the exact pixel cost of each, so it is a comparison rather than a guess.
How do I convert pixel dimensions into a ratio?
Divide both numbers by their greatest common divisor. 1920 and 1080 share 120, which gives 16:9. Awkward pairs reduce to something unreadable, so the calculator also names the closest standard ratio and prints the decimal.
Is it free, and does anything get uploaded?
It is free and there is no account. The calculator is arithmetic running in your own browser, so no image is uploaded, nothing is stored, and nothing about your frames reaches us.
Explore more
Resolutions in the studio
Which output sizes each studio offers and what changes between them.
Video resolutions explained
720p to 4K, what each is for, and when the bigger file is wasted.
Editing in the browser
Trimming and reframing a clip without installing anything.
Free storyboard templates
Printable sheets in 16:9, 9:16, square and 4:3.
Everything in the studio
Images, video, music, editing and Storyboard in one place.
Plans and credits
What each plan includes and what a generation costs.
Get the frame rightbefore you make it
The calculator is here whenever you need it. When you are ready to make the shot rather than measure it, PrismPoster generates images, video and music at the frame you choose.