Design calculator
Aspect Ratio Calculator
Reduce image, video, and screen dimensions to an aspect ratio.
Enter positive pixel or physical dimensions.
Aspect ratio
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How width and height become a ratio
Both width and height must be positive numbers. When both are whole numbers, the calculator finds their greatest common divisor with the Euclidean algorithm and divides both sides by it, producing a simplified ratio like "16:9". When either value has a decimal, a GCD-based simplification no longer makes sense, so the calculator instead reports a decimal ratio scaled to 1, such as "1.7778:1".
A second line underneath always shows the raw decimal ratio — width divided by height — to six decimal places, regardless of which format the main result takes.
The GCD walk-through for 1920 × 1080
The Euclidean algorithm on 1920 and 1080: 1920 = 1×1080 + 840, then 1080 = 1×840 + 240, then 840 = 3×240 + 120, then 240 = 2×120 + 0. The last nonzero remainder, 120, is the greatest common divisor.
Dividing both dimensions by 120 gives 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so 1920×1080 simplifies to 16:9 — matching the decimal ratio of 1920 ÷ 1080 = 1.777778.
Letterboxing and pillarboxing math
Fitting 16:9 footage inside a 4:3 frame at a shared width of 1920px: a 4:3 frame at that width needs a height of 1920 × 3 ÷ 4 = 1440px, but the 16:9 footage is only 1080px tall, leaving 1440 − 1080 = 360px of empty space, split evenly into 180px black bars above and below the video.
The reverse case, fitting 4:3 footage inside a 16:9 frame at a shared height of 1080px: the 4:3 content is 1080 × 4 ÷ 3 = 1440px wide, while the 16:9 frame is 1920px wide, leaving 1920 − 1440 = 480px split into 240px bars on either side.
Everyday aspect ratio examples
- 1920×1080 and 2560×1440 both simplify to 16:9 — 1440p is the same shape as 1080p, just with more pixels (their greatest common divisor is 160).
- A square Instagram post at 1080×1080 simplifies to 1:1, since the greatest common divisor of two equal numbers is the number itself.
- A vertical phone video at 1080×1920 simplifies to 9:16, the width-and-height reversal of standard widescreen.
- A 35mm-style photo at 3000×2000 simplifies to 3:2, since their greatest common divisor is 1000.
- US letter paper at 8.5×11 inches has non-whole dimensions, so the calculator reports a decimal ratio of 0.7727:1 instead of a simplified fraction (8.5 ÷ 11 = 0.772727).
Frequently asked questions
Why does 1920×1080 show as "16:9" but 8.5×11 shows as a decimal?
The colon-separated simplification only runs when both numbers are whole. Decimal inputs like 8.5 have no meaningful greatest common divisor, so the calculator falls back to a plain width-to-height decimal instead.
What is the greatest common divisor doing in this calculation?
It's the largest number that divides both width and height evenly. Dividing 1920 and 1080 by their greatest common divisor of 120 produces the smallest whole-number pair — 16 and 9 — that represents the identical shape.
How much letterboxing does 16:9 video get inside a 4:3 frame?
At a shared 1920px width, a 4:3 frame is 1440px tall but the 16:9 video is only 1080px tall, leaving 180px black bars on the top and bottom.
Are 1080p and 1440p the same aspect ratio?
Yes. 1920×1080 and 2560×1440 both simplify to 16:9, since 2560 and 1440 share a greatest common divisor of 160 — 1440p is a higher-resolution version of the same 16:9 shape.
Why does the calculator reject a width or height of zero?
A ratio needs two positive quantities to compare, and dividing by a zero height is undefined, so both fields require a value greater than zero before a result appears.
How do I use this for cropping a photo to a target ratio?
Enter your target ratio's two numbers as width and height to see its decimal form, then multiply that decimal by whichever side of your source photo you're keeping fixed to find the matching crop length for the other side.