What is an aspect ratio?

The width-to-height proportion of a rectangle, expressed as the smallest pair of whole numbers that describe it. 1920×1080 reduces to 16:9 because gcd(1920, 1080) = 120, and 1920/120 = 16, 1080/120 = 9.

Does the ratio depend on units?

No. Aspect ratio is dimensionless — 16:9 in pixels, inches, or arbitrary design units all describe the same shape.

How does the scale-to-fit work?

Pick whichever dimension you want to lock, type its value, and the calculator returns the other dimension at the same ratio. Useful for export presets — 1920 wide at 16:9 must be 1080 tall.

Why is my dimension off by one pixel after scaling?

Sub-pixel dimensions are rounded to the nearest integer. For tight design layouts this is usually fine; if you need exact dimensions, pick locked values whose ratio resolves cleanly.

Are 1.85:1 or 2.39:1 'real' aspect ratios?

Yes — those are cinema standards. They're often quoted as decimals because the reduced integer form is awkward (1.85:1 reduces to 37:20). The calculator handles them but the preset list uses the decimal label for recognisability.

What about pixel aspect ratio vs display aspect ratio?

Most modern displays have square pixels, so the two are identical. Some older video formats (anamorphic widescreen DVD, 1080i broadcast feeds) store non-square pixels — there the display aspect ratio is different from the storage aspect ratio. Convertitive treats inputs as square pixels.

Aspect Ratio Calculator

Width and height in, ratio + scaled dimensions + preview out.

Aspect ratio describes the relationship between a rectangle’s width and height as a reduced fraction. 1920×1080 is 16:9; 1080×1920 is 9:16. The calculator below reduces any pair of dimensions to its lowest terms, previews the resulting rectangle, and lets you scale to a new size while keeping the ratio locked — useful for picking export sizes, designing responsive components, and producing letterbox-free video crops.

Width (px)

Height (px)

Aspect ratio

16:9

≈ 1.7778

Scale this ratio to a new size

Lock either dimension, get the other one back at the same aspect.

1280 × 720 px

Common presets

How to use

Enter width and height
Use raw pixels, design units, or any positive numbers — only the ratio matters. The reduced form updates as you type.
Read the result
Both the reduced fraction (e.g. 16:9) and the decimal (≈ 1.778) are shown. The preview rectangle has exactly that shape.
Scale to a new size
Lock width or height in the scaling card, type the value you want it to take, and the calculator returns the other dimension at the same ratio.

Where each ratio shows up

Ratio	Typical use
16:9	YouTube, HDTV, most laptop screens, ‘widescreen’
9:16	Instagram Reels, TikTok, Stories, vertical phone video
4:3	Older TVs, classroom projectors, iPad screens
3:2	35mm photography, DSLR sensors
1:1	Instagram square posts, profile photos, podcast cover art
21:9	Ultrawide monitors, gaming widescreen
2.39:1	Anamorphic cinema (most modern feature films)

Frequently asked questions

What is an aspect ratio?: The width-to-height proportion of a rectangle, expressed as the smallest pair of whole numbers that describe it. 1920×1080 reduces to 16:9 because gcd(1920, 1080) = 120, and 1920/120 = 16, 1080/120 = 9.
Does the ratio depend on units?: No. Aspect ratio is dimensionless — 16:9 in pixels, inches, or arbitrary design units all describe the same shape.
How does the scale-to-fit work?: Pick whichever dimension you want to lock, type its value, and the calculator returns the other dimension at the same ratio. Useful for export presets — 1920 wide at 16:9 must be 1080 tall.
Why is my dimension off by one pixel after scaling?: Sub-pixel dimensions are rounded to the nearest integer. For tight design layouts this is usually fine; if you need exact dimensions, pick locked values whose ratio resolves cleanly.
Are 1.85:1 or 2.39:1 'real' aspect ratios?: Yes — those are cinema standards. They're often quoted as decimals because the reduced integer form is awkward (1.85:1 reduces to 37:20). The calculator handles them but the preset list uses the decimal label for recognisability.
What about pixel aspect ratio vs display aspect ratio?: Most modern displays have square pixels, so the two are identical. Some older video formats (anamorphic widescreen DVD, 1080i broadcast feeds) store non-square pixels — there the display aspect ratio is different from the storage aspect ratio. Convertitive treats inputs as square pixels.

About

History of widescreen

Pre-1953 movies were 4:3 (1.33:1). When television adopted that ratio, Hollywood moved to 1.85:1 and 2.35:1 anamorphic to give people a reason to leave the house. HDTV in the 1990s adopted 16:9 as a compromise between film widescreen and pre-existing TV. Mobile flipped the script in the 2010s — now 9:16 is the dominant ratio for the most-watched video on Earth.

Practical SEO note

Search engines prefer images with a known aspect ratio — Open Graph requires 1200×630 (≈ 1.91:1), Twitter Cards accept 16:9 or 2:1, schema.org structured-data prefers 16:9, 4:3, and 1:1. Designing exports to those exact dimensions avoids ugly automatic crops on social previews.