It’s 11pm, the client wants a 2.39:1 version of the spot inside a 1920 x 1080 frame, and you need to know exactly how tall the bars are before you build the matte. Or someone sends you a 1350 x 1080 file and asks what ratio that even is. The aspect ratio cheat sheet covers the standard sizes. This page covers everything the sheet doesn’t: type in any numbers, get the answer.
There are four tools below and none of them send anything anywhere. The result goes into the page address as you type, so you can copy the link and paste it into the Slack thread where the question came from.
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What each tool answers
The first tab takes a resolution and gives you the ratio. Type a width and height and you get the reduced ratio, the decimal version, the pixel count, and the closest named standard within half a percent. So 4096 x 2160 comes back as 256:135, which is 1.90:1, which is DCI 4K. And 1350 x 1080 is 5:4, an old broadcast shape that still shows up in archive projects. If either number is odd you get a warning, because most encoders want even dimensions.
The second tab goes the other way. Pick a ratio, lock the width or the height, and the tool fills in the other side. Scope at 1920 wide is 1920 x 804 rounded to even pixels, or 1920 x 800 if you switch the rounding to mod-16. Vertical 9:16 at 1920 tall is 1080 x 1920. The preset list has the shapes clients ask for by name, and there’s a custom field for anything else, in either 21:9 or 2.35:1 form.
The third tab is the letterbox and pillarbox math. Give it the picture ratio and the frame you’re delivering in, and it returns the active picture size, the bar size on each side, and where the picture starts. 2.39:1 inside 1920 x 1080 is a 1920 x 804 picture with 138-pixel bars top and bottom. 4:3 inside the same frame is 1440 x 1080 with 240-pixel pillars. A 16:9 clip dropped into a 1080 x 1920 vertical frame keeps only 1080 x 608 of picture, with 656 pixels of empty space above and below, which is why your horizontal footage looks so small in a Reel.
The fourth tab does safe areas. Any frame size in, the action-safe and title-safe rectangles out, in pixels, with the margins. The tool uses the same 93 percent and 90 percent convention the cheat sheet does. In 1080p that’s 1786 x 1004 for action and 1728 x 972 for titles, with 96 pixels of side margin and 54 on top and bottom for the title box.
Why the rounding matters
Divide 1920 by 2.39 and you get 803.35. You can’t export a third of a pixel, so every result on this page is rounded to an even number by default. H.264 and HEVC encode in blocks, and an odd frame dimension is the fastest way to get a green line down one edge or an export that fails at 99 percent. Mod-16 is the stricter version of the same rule from the older codec days: dimensions divisible by 16 line up with the macroblock grid, so nothing gets padded. Modern encoders handle mod-2 without complaint, but if a delivery spec says mod-16, the toggle is there.
The rounding is also why two people can calculate the same ratio and land on different numbers. 2.39:1 at 1920 wide is 804 tall with even rounding and 800 tall with mod-16. Both play fine and both sit within half a percent of true scope. If a client’s spec sheet lists one and you deliver the other, nobody will see the difference, but the QC report might flag it, so match the sheet.
The two 4Ks, again
Type 3840 x 2160 and 4096 x 2160 into the first tool back to back and you’ll see the whole DCI-versus-UHD problem in two rows. UHD is 16:9. DCI 4K is 1.90:1, a slightly wider container that cinema projectors use, and the flat and scope masters that live inside it are 3996 x 2160 and 4096 x 1716. Camera menus call all of these “4K.” Delivery specs don’t. The cheat sheet has the full DCI versus UHD breakdown if you need the background before you commit a timeline setting.
The rest of the reference shelf
This calculator pairs with three other pages I keep open on delivery days. The delivery specs cheat sheet has the per-platform export settings, so once you know the frame size here you can look up the codec and bitrate there. The frame rate cheat sheet covers the other axis of the same conversation. And the video storage calculator tells you how many gigabytes per hour that frame size costs you at each codec, which matters before you promise a client a 4K master by Friday.
If the tool gives you a number that doesn’t match a spec sheet you’ve been handed, trust the spec sheet and match it. The math here is right, but the person paying the invoice gets to pick the rounding. And if you hit a ratio or a case the calculator doesn’t handle, leave a comment and I’ll add it.
