About Pixel Aspect Ratio
Pixel aspect ratio (PAR) is the width-to-height ratio of a single pixel, not of the whole image. It matters because a file's pixel dimensions (its storage resolution) do not always represent a picture made of square pixels — some formats deliberately use rectangular pixels, so the raw width ÷ height of the pixel grid (the storage aspect ratio, SAR) can differ from how the picture actually looks once it is displayed (the display aspect ratio, DAR).
The formula
The three quantities are tied together by one standard equation used throughout video and image engineering:
DAR = SAR × PAR
- Storage Aspect Ratio (SAR) = storage width (px) ÷ storage height (px) — the raw pixel-grid ratio.
- Pixel Aspect Ratio (PAR) = width of one pixel ÷ height of one pixel — how "square" or "stretched" each individual pixel is.
- Display Aspect Ratio (DAR) = SAR × PAR — how the image looks once it is displayed with the correct pixel shape.
Rearranging the formula lets you solve for whichever value is unknown: PAR = DAR ÷ SAR, or SAR = DAR ÷ PAR. This calculator takes a storage resolution and a PAR, computes SAR and DAR directly, and also reports the equivalent size the image would need if every pixel were made square — the storage width multiplied by PAR, with the height unchanged.
Why pixels aren't always square
Square pixels (PAR 1:1) are standard on virtually all modern digital cameras, phones, and computer monitors, so storage aspect ratio and display aspect ratio are simply the same number. Non-square pixels exist mainly for historical broadcast-video reasons: analog-derived digital video standards such as NTSC and PAL sampled a fixed number of pixels per line regardless of the target screen shape, so the resulting pixel grid ended up a different shape than the intended 4:3 or 16:9 picture. The pixel aspect ratio is the correction factor that reconciles the two.
Common reference values
| Format | Storage (px) | PAR | Display (DAR) |
|---|---|---|---|
| Square pixels (HD video, web, phones) | e.g. 1920×1080 | 1:1 | 16:9 |
| NTSC D-1/DV, 4:3 | 704×480 | 10:11 | 4:3 |
| NTSC D-1/DV, 16:9 | 704×480 | 40:33 | 16:9 |
| PAL D-1/DV, 4:3 | 704×576 | 12:11 | 4:3 |
| PAL D-1/DV, 16:9 | 704×576 | 16:11 | 16:9 |
Note: NTSC and PAL DV/D-1 files are frequently stored at 720 pixels wide (720×480 or 720×576). 704 pixels is the conventionally "active" picture width used to derive the PAR figures above; the extra columns at 720 correspond to horizontal blanking that is not part of the visible picture. Both widths appear in practice, so check what your specific source calls "active" before assuming exact numbers.
Practical uses
- Figuring out why footage captured or exported at one pixel size looks squeezed or stretched until the correct PAR is applied.
- Converting anamorphic or broadcast-standard video to square pixels for editing, compositing, or web delivery.
- Confirming that a target storage resolution and PAR combination actually produces the intended on-screen aspect ratio before rendering or exporting.