How to Use This Calculator

Choose a calculation type from the dropdown, enter your values, and the result appears immediately with a step-by-step breakdown. Three modes cover the most common aspect ratio tasks.

Find aspect ratio

Enter width and height in any unit (pixels, inches, centimeters, millimeters). Both values must use the same unit. The calculator finds the greatest common divisor of the two numbers, divides each by it, and returns the simplified ratio. It also shows the decimal ratio and flags the closest standard ratio if your dimensions are near a well-known size.

Find new height (keep ratio)

Enter the original width and height, then type the new width you need. The calculator returns the exact height that keeps the original proportions. Use this when resizing images for websites, scaling video thumbnails, or converting between screen resolutions without distorting the content.

Find new width (keep ratio)

The reverse of the mode above. Enter original dimensions and a target height. The calculator gives you the width that preserves the ratio. Useful when you have a fixed height constraint, such as a sidebar image slot or a banner with a set vertical dimension.

What Is Aspect Ratio?

Aspect ratio describes the proportional relationship between width and height. It tells you the shape of a rectangle, regardless of its actual size. The ratio is written as W:H (width to height).

A screen with a 16:9 aspect ratio is sixteen units wide for every nine units tall. That holds true whether the screen is 5 inches or 85 inches diagonal. The size changes; the shape does not. This is the key insight that makes aspect ratio useful.

A 1920×1080 pixel image and a 1280×720 pixel image look identical in shape because both simplify to 16:9. Scale either one to 800 pixels wide and you know the height must be 450 to avoid stretching or squashing. No guesswork needed.

The key uses are:

Displays: matching content to screen shape without black bars or stretching.
Video production: choosing a frame size that suits the platform (YouTube, TikTok, cinema).
Photography: knowing what crop to apply before printing at a specific paper size.
Web design: setting image containers that scale correctly on different screen sizes.
Print: calculating output dimensions from a scan at a given DPI.

Aspect ratio does not tell you resolution, quality, or pixel density. Two screens can share the exact same aspect ratio and have very different pixel counts and sharpness levels.

Common Aspect Ratios Explained

Most images, videos, and screens use a small set of well-known ratios. Recognizing them saves time when you need to resize or crop without distorting content.

16:9 (Widescreen)

The universal standard for modern video and screens. Every HD resolution uses it: 1920×1080 (Full HD), 2560×1440 (QHD), 3840×2160 (4K UHD), and 1280×720 (720p). YouTube, Netflix, Zoom calls, and most streaming platforms default to 16:9. The decimal equivalent is approximately 1.778. If you are producing video for any major platform, this is your starting ratio.

4:3 (Traditional)

The standard television ratio before widescreen arrived. You still see it on older monitors, many iPad models, and some compact cameras. Resolutions like 1024×768 and 800×600 use it. If you are cropping old home video or designing for legacy display hardware, 4:3 comes up regularly. Decimal: 1.333.

1:1 (Square)

Equal width and height. Instagram's original post format uses it, as do most social media profile photos and app icons. Graphic design for tiles and album artwork often targets 1:1 because it works in both landscape and portrait contexts without visible cropping.

3:2 (Photography)

The native sensor format for most DSLR and mirrorless cameras, inherited from 35mm film (36mm × 24mm). A 24-megapixel Canon shoots at 6000×4000, a 45-megapixel Sony at 8064×5376, both 3:2. Standard photo print sizes like 6×4 inches and 12×8 inches also use this ratio. Decimal: 1.5.

9:16 (Vertical video)

The portrait-orientation counterpart to 16:9. TikTok, Instagram Reels, YouTube Shorts, and phone video shot in portrait mode use 9:16. A 1080×1920 frame fits this ratio exactly. With short-form vertical video growing fast, this format is now as common as its landscape equivalent for social content.

4:5 (Instagram portrait)

Instagram's recommended portrait ratio for feed posts. At 1080×1350 pixels, it takes up more vertical space in the feed than a square post, which means more screen coverage before a user scrolls past. Photographers who optimize crops for engagement often target this ratio.

21:9 (Ultrawide)

Used by gaming monitors, ultrawide desktop displays, and some cinema projection formats. Common resolutions are 2560×1080 and 3440×1440. The decimal is approximately 2.33, close to the anamorphic cinema scope ratio of 2.39:1 used in wide-release films.

16:10 (Wide laptop)

Common on MacBook laptops and many business monitors. Resolutions like 2560×1600 and 1920×1200 use this ratio. Slightly taller than 16:9, it provides more vertical room for documents, code editors, and spreadsheets. Decimal: 1.6.

How to Calculate Aspect Ratio

The calculation relies on the greatest common divisor (GCD), the largest integer that divides evenly into both the width and the height.

Aspect Ratio = (Width ÷ GCD) : (Height ÷ GCD)

Step-by-step: 1920×1080

Use the Euclidean algorithm to find the GCD. Repeatedly divide the larger number by the smaller and take the remainder, until the remainder is zero.

1920 ÷ 1080 = 1 remainder 840
1080 ÷ 840 = 1 remainder 240
840 ÷ 240 = 3 remainder 120
240 ÷ 120 = 2 remainder 0 → GCD = 120

Width: 1920 ÷ 120 = 16. Height: 1080 ÷ 120 = 9. Aspect ratio: 16:9.

The decimal method

Divide width by height to get the decimal ratio. 1920 ÷ 1080 = 1.7778. Match this to a known value: 16 ÷ 9 = 1.7778. The decimal method is faster when you just need to identify the ratio family rather than the exact simplified fraction.

Common decimal fingerprints: 1.333 = 4:3, 1.5 = 3:2, 1.6 = 16:10, 1.778 = 16:9, 2.333 = 21:9. Memorizing these four covers the vast majority of screens and cameras you will encounter.

Scaling formula

Once you have the ratio, scaling is straightforward. To keep proportions when changing one dimension:

New height = new width × (original height ÷ original width)

This is the same cross-multiplication used in any proportion problem. The Slope Calculator uses similar ratio logic when expressing rise over run as a simplified fraction.

Aspect Ratio for Pixels and Screens

Resolution and aspect ratio are not the same thing. Resolution counts pixels. Aspect ratio describes shape. A 4K screen (3840×2160) and a standard HD screen (1920×1080) have identical 16:9 ratios but vastly different pixel counts and sharpness.

This distinction matters for practical work. A 1280×720 YouTube thumbnail and a 3840×2160 one look identical in shape. Both fit the 16:9 player without letterboxing. You can crop a photo to any aspect ratio at full resolution, then scale the result later, and the shape stays the same throughout.

Square pixels vs non-square pixels

Most modern digital displays use square pixels, where each pixel is as wide as it is tall. Older broadcast standards (DV video, DVD) sometimes used non-square pixels. A DV frame at 720×480 appears to be 3:2 by pixel count but displays at 4:3 because each pixel has a width-to-height ratio of 0.9. If you notice a video looking slightly squashed in an editor, non-square pixels are the usual cause.

CSS aspect ratio

Web developers often need to maintain a container's aspect ratio as it scales. The CSS property aspect-ratio: 16 / 9; keeps an element proportional at any width. Before this property existed, the padding-top hack used padding-top: 56.25% (which is 9 ÷ 16 × 100). The Percentage Calculator can verify that calculation or help you find the correct padding percentage for any custom ratio.

Aspect Ratio in Photography and Video

Camera sensors and film formats largely dictate the aspect ratios photographers work with. Knowing your sensor ratio saves time when cropping for print or social media.

Camera sensor ratios

35mm full-frame sensors (Canon EOS R series, Nikon Z series, Sony A7 series) shoot natively at 3:2. The name comes from 35mm film, where the image frame measured 36mm × 24mm. Divide 36 by 24 and you get 1.5, the decimal for 3:2. Micro Four Thirds cameras (Panasonic, OM System) shoot at 4:3 natively, matching older televisions and iPads.

Medium format cameras (Hasselblad X series, Fujifilm GFX) often use 4:3 or sensor-specific ratios. Some square-format medium format systems shot at 1:1, which is where the classic square photo aesthetic in editorial and fashion photography originates.

Video and cinema formats

Video standards by platform and use case:

Broadcast television (modern): 16:9
Vertical social video (TikTok, Reels, Shorts): 9:16
Cinema scope (major studio films): 2.39:1
Academy flat (independent and prestige film): 1.85:1
IMAX: approximately 1.43:1 in its native format
Anamorphic widescreen: shot at a squeezed ratio, de-squeezed in post to produce 2.39:1

If you are producing content for multiple platforms, the Triangle Calculator will not help with ratios, but the geometric thinking is the same: you are working with proportional relationships between two dimensions. And when calculating how much larger a new canvas is compared to the original as a percentage, the Percentage Calculator handles that directly.

Worked Examples

Example 1: Full HD Monitor (1920×1080)

A monitor lists its resolution as 1920×1080. What is its aspect ratio?

GCD(1920, 1080) = 120. Width: 1920 ÷ 120 = 16. Height: 1080 ÷ 120 = 9. Aspect ratio: 16:9. This is the universal widescreen standard for HDTVs, monitors, and streaming video.

Example 2: Resize a 1280×720 Image to 1920 Pixels Wide

A video thumbnail is 1280×720. A client needs a version at 1920 pixels wide. What height preserves the ratio?

New height = 1920 × (720 ÷ 1280) = 1920 × 0.5625 = 1080 pixels. The result is 1920×1080, still 16:9. Scale factor is 1.5×.

Example 3: DSLR Photo at 6000×4000

A Canon R5 shoots at 6000×4000 pixels. What is the aspect ratio?

GCD(6000, 4000) = 2000. Width: 6000 ÷ 2000 = 3. Height: 4000 ÷ 2000 = 2. Aspect ratio: 3:2. Standard full-frame sensor ratio, matching 35mm film. A 6×4 inch print uses exactly this ratio.

Example 4: TikTok Video at 1080×1920

A phone records video in portrait at 1080×1920. What is the aspect ratio?

GCD(1080, 1920) = 120. Width: 1080 ÷ 120 = 9. Height: 1920 ÷ 120 = 16. Aspect ratio: 9:16. The standard vertical video format used by TikTok, Instagram Reels, and YouTube Shorts.

Example 5: Find the Height for a 3:2 Print at 12 Inches Wide

You need to print a 3:2 image at exactly 12 inches wide. What height do you need?

New height = 12 × (2 ÷ 3) = 12 × 0.6667 = 8 inches. A 12×8 inch print. This is a standard consumer photo print size, derived directly from the 3:2 sensor ratio of most cameras.

Frequently Asked Questions

What is aspect ratio?

Aspect ratio is the proportional relationship between a rectangle's width and height, written as W:H. It describes shape, not size. A 1920×1080 screen and a 1280×720 screen both have a 16:9 aspect ratio, even though one is much higher resolution than the other.

How do I calculate aspect ratio from width and height?

Find the greatest common divisor (GCD) of the width and height, then divide each number by the GCD. For 1920×1080: GCD is 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9. The aspect ratio is 16:9. This calculator does that calculation automatically.

What is the aspect ratio of 1920×1080?

16:9. Divide both numbers by their GCD of 120 to get 16 and 9. This is the universal widescreen standard used by HDTVs, most monitors, YouTube, and most streaming platforms. The decimal equivalent is 1.778.

How do I calculate aspect ratio in pixels?

The process is identical to any other unit. Find GCD of the pixel width and pixel height, divide each by it. For 3840×2160 (4K UHD): GCD = 120, so 3840 ÷ 120 = 32 and 2160 ÷ 120 = 18. Both 32 and 18 are divisible by 2, simplifying further to 16:9.

What aspect ratio is 4K?

Standard consumer 4K UHD (3840×2160) is 16:9. Cinema 4K (4096×2160, DCI 4K) has a ratio of 256:135, often described as approximately 17:9. Most 4K TVs and monitors use 16:9. If someone says "4K" without qualification, they almost always mean 3840×2160 at 16:9.

How do you resize an image while keeping the aspect ratio?

Multiply the new width by the ratio of original height to original width: new height = new width × (original height ÷ original width). To resize 1280×720 to 800 pixels wide: 800 × (720 ÷ 1280) = 800 × 0.5625 = 450. New dimensions: 800×450. The "Find new height" mode in this calculator does this instantly.

What is a 16:9 aspect ratio in pixels?

Any resolution where width ÷ height = 1.778 is 16:9. Common examples: 1280×720 (720p), 1920×1080 (1080p), 2560×1440 (1440p), 3840×2160 (4K). You can verify any resolution using the "Find aspect ratio" mode above.

How do I calculate tire aspect ratio?

Tire aspect ratio is the sidewall height as a percentage of the tread width. On a tire labeled 225/55R17, the 55 is the aspect ratio: the sidewall height is 55% of the 225mm tread width. Sidewall height = 225 × 0.55 = 123.75mm. This is a different calculation from image or screen aspect ratios, closer to a standard percentage problem than a ratio simplification.

What is the aspect ratio of an A4 sheet of paper?

A4 paper is 210mm × 297mm. GCD(210, 297) = 3, giving 70:99. The decimal ratio is 1:1.414, which is the square root of 2. The entire ISO 216 paper series (A0, A1, A2, A3, A4...) is designed so that folding any sheet in half gives the next smaller size with the same aspect ratio. That is a clever consequence of the square-root-of-2 ratio.

What is the difference between aspect ratio and resolution?

Resolution is the number of pixels (1920×1080 = 2,073,600 pixels total). Aspect ratio is the shape expressed as a simplified ratio (16:9). Two screens can share the same aspect ratio and have completely different resolutions, pixel densities, and image sharpness. Aspect ratio tells you nothing about quality, only proportion.

How do I calculate aspect ratio from inches?

Divide width by height to get the decimal, then match to a known ratio. An 8.5×11 inch sheet: 8.5 ÷ 11 = 0.773. For the exact simplified ratio, multiply both dimensions by 10 to get integers (85 × 110), find GCD(85, 110) = 5, giving 17:22. This is distinct from the standard photo print sizes, which use 3:2 or 4:3.

References

Adobe Photoshop: Image Size and Resolution: Official Adobe documentation covering pixels, aspect ratio, resolution, and scaling in practical image editing.
MDN Web Docs: CSS aspect-ratio property: Technical reference for the CSS aspect-ratio property and how browsers handle proportional scaling of elements.
B&H Photo: Understanding Aspect Ratios in Photography: Photography-focused overview of sensor formats, common ratios, and their effect on print and digital output.

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