How this instrument works
Pixel aspect ratio (PAR) describes the shape of a single pixel, not the shape of the whole frame. Most images assume square pixels, where PAR is 1:1 and the frame's overall shape — its display aspect ratio, or DAR — matches the raw pixel grid's own width-to-height shape, called the storage aspect ratio, or SAR. The three quantities are linked by SAR × PAR = DAR, which rearranges to PAR = DAR ÷ SAR — exactly the formula this instrument computes.
Non-square pixels exist because some video formats store a pixel grid that doesn't match their intended display shape, usually for compatibility or bandwidth reasons rooted in broadcast engineering history. The clearest example: Sony and Canon HDV camcorders record a 1440×1080 pixel grid but display it stretched to fill a 16:9 frame. The storage grid's own ratio is 1440/1080 = 4:3, while the intended display ratio is 16:9, so PAR = (16/9) ÷ (4/3) ≈ 1.333 — each pixel needs to be one-third wider than it is tall for the footage to look correct.
This still matters in real editing workflows: software like Premiere Pro, Final Cut and DaVinci Resolve needs the correct PAR set on a clip, or non-square-pixel footage displays visibly squeezed or stretched until it's corrected. Anamorphic cinema lenses and a handful of legacy broadcast and DVD formats also rely on non-square pixel grids deliberately, so PAR isn't purely a historical curiosity even in modern pipelines.
- Enter your frame's intended display shape as two numbers into Frame aspect ratio — width part and Frame aspect ratio — height part, e.g. 16 and 9.
- Enter the actual pixel grid your file stores into Pixel grid width (px) and Pixel grid height (px), e.g. 1440 and 1080.
- Read Pixel aspect ratio (PAR) directly beneath the inputs.
- A PAR of 1.0 means square pixels — no correction needed. Any other value means each pixel must be stretched or squeezed by that factor to display at the correct frame shape.
- If your editing software doesn't auto-detect PAR from the file, enter this value manually in its clip interpretation or footage properties settings.
Worked example — 640×480 VGA in a 4:3 frame
Enter 4 and 3 into the frame aspect ratio fields, then 640 and 480 into the pixel grid fields — a VGA image meant to fill a 4:3 frame. The storage aspect ratio (640/480) equals 4/3 exactly, the same as the display aspect ratio, so PAR = (4/3) ÷ (4/3) = 1.0. Pixel aspect ratio reads 1.0, the reference 'square pixel' case every other PAR value is measured against.
Contrast that with a Sony or Canon HDV camcorder, which records a 1440×1080 pixel grid into a 16:9 frame: DAR = 16/9, SAR = 1440/1080 = 4/3, so PAR = (16/9) ÷ (4/3) ≈ 1.333 — each pixel is one-third wider than it is tall, a well-documented quirk of the DV/HDV broadcast format that editing software must correct for.
Questions
What's the difference between pixel aspect ratio and display aspect ratio?
Display aspect ratio (DAR) is the shape you actually see on screen — the frame's intended proportions, like 16:9. Pixel aspect ratio (PAR) is the shape of one individual pixel within the stored file. When PAR is 1 (square pixels), the raw pixel grid's own shape matches the display shape directly; when PAR isn't 1, the pixel grid and the display shape differ, and stretching each pixel by PAR is what reconciles them.
Why would a video file use non-square pixels at all?
Mostly for compatibility and bandwidth reasons rooted in broadcast engineering history. Standard-definition DV and HDV formats stored a fixed pixel grid — like 720×480 or 1440×1080 — regardless of whether the footage was meant to display at 4:3 or 16:9, so the same hardware and codec could serve both shapes just by changing how the pixels were stretched on playback, rather than needing a different grid for each.
What happens if I import footage with the wrong PAR set?
The footage displays visibly squeezed or stretched — circles look like ovals, and anything that should be square looks rectangular. Editing software like Premiere Pro, Final Cut or DaVinci Resolve usually reads PAR metadata automatically from known formats, but if it's missing or wrong, you'll need to set the correct PAR manually in the clip's interpretation settings to fix the distortion.
Is PAR still relevant with modern 4K/HD video?
Less often, but not never. Most modern cameras and codecs record square-pixel (PAR = 1.0) footage by default, so the concept fades into the background for everyday HD and 4K work. It resurfaces with anamorphic cinema lenses, which deliberately squeeze a wider image onto a square-pixel sensor, and with some legacy broadcast, DVD and archival formats that still carry non-square pixel grids.
How do I know my pixel grid (SAR) versus my frame ratio (DAR)?
Your pixel grid is the file's actual stored resolution — what you'd see in a 'video properties' or 'media info' panel, such as 1440×1080. Your intended frame ratio (DAR) is the shape the footage is supposed to display at, which for most consumer HDV footage is 16:9 even though the stored grid is 4:3 in proportion — that mismatch is exactly what PAR corrects for.