Aspect Ratio Calculator
Calculate the missing dimension of an aspect ratio and see how it compares with common formats.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
An aspect ratio describes the relationship between width and height, so scaling one dimension requires scaling the other by the same factor. That is why resizing a video without preserving the ratio stretches or crops the image.
Worked example
calculated with the default values below
Known width 1,920 px · Ratio width part 16 · Ratio height part 9 · Target width 1,280 px · Known height 1,080 px Height for that width 1,080.0 px · Decimal ratio 1.7778 · Height for the target width 720.0 px · Ratio from your dimensions 16:9 · Closest common format 16:9 (HD widescreen) · Pixel area 2,073,600 px²
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
h = W × r_h ÷ r_w
- W
- Known or target width
- r_w
- Ratio width part
- r_h
- Ratio height part
- h
- Computed height
The ratio from your dimensions is obtained by dividing rounded width and height by their greatest common divisor.
Frequently asked questions
Why must height scale with width to keep a 16:9 frame?
The decimal ratio is ratio width ÷ ratio height, so 16:9 gives 1.778, and any width divided by that yields the matching height. Feed 1920×1080 and a target width of 1280, and the height becomes 720, never 1080, because stretching height independently distorts the image. The closest-format check also flags when your numbers round to 21:9 or 4:3 instead.