Image Ratio Calculator — Aspect Ratio & Proportional Scaling
Calculate the aspect ratio of any image from its pixel dimensions. The calculator simplifies the ratio to its lowest whole-number form (e.g. 1920×1080 → 16:9) and lets you scale to any new width while keeping the proportions exact.
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- 1
Greatest common divisor
GCD(1,920, 1,080) = 120Euclidean algorithm — largest integer that divides both width and height exactly. - 2
Simplified ratio
1,920 ÷ 120 : 1,080 ÷ 120 = 16:9 - 3
Scaled height
1,280 ÷ 1.7778 = 720 px
How does this calculator work?
Aspect ratio = W : H divided by their GCD. A 1920×1080 image simplifies to 16:9 (GCD = 120). To scale to a new width, proportional height = new width × (H ÷ W). Total pixels = width × height; divide by 1,000,000 for megapixels.
Formula
How this is calculated
The aspect ratio describes the proportional relationship between width and height. To simplify it to its canonical form (like 16:9 rather than 1920:1080), both dimensions are divided by their Greatest Common Divisor (GCD) — the largest number that divides both without a remainder. This is computed using the Euclidean algorithm: repeatedly replace the larger number with the remainder of dividing the larger by the smaller, until the remainder is zero.
To scale an image to a different width while maintaining the original proportions, divide the original width by the original height to get the decimal ratio, then multiply the new width by that ratio to find the required height. For example, a 1920×1080 image scaled to 1280px wide needs a height of 1280 ÷ (1920/1080) = 720px.
The megapixel count is simply total pixels (width × height) divided by one million. A 1920×1080 image has about 2.07 megapixels. Megapixels are useful for comparing sensor resolutions and estimating maximum print sizes.
Frequently asked questions
16:9 means for every 16 pixels of width there are 9 pixels of height — a widescreen shape. It became the dominant standard for HD television (720p, 1080p) and computer displays because it efficiently fills wide screens, matches cinema's widescreen formats, and offers a good balance between horizontal content and vertical space.
Divide your original width by its height to get the decimal ratio. Then multiply your new width by this ratio to get the correct height (or divide by it if you're given the new height). This calculator does this automatically: enter your original dimensions and the desired new width to get the proportional height.
The GCD simplification gives the mathematically exact reduced form. For 1920×1080, GCD = 120, giving 16:9. For unusual resolutions like 1366×768, GCD = 2 giving 683:384 — a ratio that doesn't correspond to a standard name. Many displays use non-standard resolutions that don't reduce to tidy ratios.
Also known as
TG we-Calculate Editorial Team. (2026). Image Ratio Calculator — Aspect Ratio & Proportional Scaling [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/image-ratio-calculator
TG we-Calculate Editorial Team. "Image Ratio Calculator — Aspect Ratio & Proportional Scaling." TG we-Calculate. 2026. https://we-calculate.com/calculator/image-ratio-calculator.
TG we-Calculate Editorial Team, "Image Ratio Calculator — Aspect Ratio & Proportional Scaling," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/image-ratio-calculator
@misc{wecalculate_image_ratio_calculator, title = {Image Ratio Calculator — Aspect Ratio & Proportional Scaling}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/image-ratio-calculator}}, year = {2026}, note = {TG we-Calculate} }
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