Aspect Ratio Calculator

To resize an image without stretching or squashing it, you need to preserve its aspect ratio — the proportional relationship between width and height. This calculator finds the largest size that fits entirely inside a target width and height while keeping that same ratio, which is the standard "fit" (contain) behavior used in most editing and web-display tools.

The calculation finds a single scale factor: the smaller of (target width ÷ image width) and (target height ÷ image height), then applies that factor to both dimensions. Using the smaller ratio guarantees the scaled image fits inside the target box on both axes.

Example: a 4000 × 3000 pixel photo (4:3 ratio) resized to fit inside a 1200 × 1200 box scales down to 1200 × 900 — the width fills the box while the height leaves a margin, because the source image is wider than it is tall.

Social crops (1:1, 4:5, 9:16) often trim edges of 3:2 camera files — plan composition with safe margins.

Fit-inside vs fill-crop modes behave differently — this tool scales to fit within a box preserving ratio.

Worked example: 4000×3000 (4:3) fit inside 1200×1200 → 1200×900.

Instagram feed posts favor 4:5 vertical (1080×1350) while Stories use 9:16 — a 3:2 camera file scaled to fit 1200×1200 (default target box) leaves horizontal letterboxing unless you crop intentionally in post. Instagram 4:5 vertical trims 3:2 camera files — plan headroom when scaling 4000×3000 into 1200×1200 square export templates.

Anamorphic video lenses capture wider aspect ratios than sensor native — this tool handles still rectangular pixels, not desqueeze metadata from 2× anamorphic glass on cinema bodies. Anamorphic desqueeze is out of scope — this tool handles rectangular still pixels, not 2× cinema glass metadata on video frames. Export a crop-safe master when social deliverables must survive 4:5 and 9:16 reframes from one file.

A four-thousand by three-thousand pixel source scaled to fit inside a 1200×1200 box becomes 1200×900 — expect about 150 px letterbox margin top and bottom when centered in a square export template for mixed Instagram carousel aspect ratios. Social editors often export at 1080 wide for feed posts after confirming the scaled height still clears text overlays.