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About this tool
Work out exact letterbox or pillarbox bar sizes when fitting one aspect ratio inside another frame, in pixels and percent.
This calculator fits a picture of one aspect ratio inside a frame of another without cropping, then reports the black bar size in pixels and percent. When the source is wider than the frame the picture height becomes frame width divided by the source ratio and the leftover splits into two horizontal letterbox bars; when it is narrower the picture width becomes frame height times the source ratio and the bars are vertical pillarbox. Editors, motion designers and social media teams use it to place graphics and titles clear of the bars.
Open Letterbox Pillarbox Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Bar size, picture size and percentages from one pair of ratios
Also gives the picture size rounded down to even pixels for H.264 and H.265
A scaled preview shows letterbox or pillarbox before you build the sequence
About 138 pixels top and bottom. The picture occupies 1920 / 2.39 = 803 pixels of height, leaving 277 pixels to split between two bars, and the image fills roughly 74% of the frame area.
Letterbox adds bars above and below because the source is wider than the frame, such as scope footage in a 16:9 timeline. Pillarbox adds bars at the left and right because the source is narrower, such as 4:3 or vertical video in a widescreen frame.
Yes — round the picture dimension down to an even number and let the bars absorb the remainder, because H.264 and H.265 with 4:2:0 chroma need even width and height. Stretching the picture to remove a one-pixel gap introduces visible distortion.
Only by cropping or by reframing: scaling the picture to cover the frame removes the bars but cuts off the edges, which is a crop calculation rather than a fit. Many social platforms expect a full-bleed frame, so shooting or reframing for the delivery ratio is usually better than baking bars in.
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