Aspect Ratio Calculator: Find Screen & Image Ratios

This calculator works out the aspect ratio of a screen, image, or video from its width and height, and it also gives the missing dimension when you scale one side to a new size. You enter the width and height in any unit (pixels, cm, inches), and you get back the simplified ratio (like 16:9) and the missing width or height for a target ratio. The first result shown is the simplified aspect ratio, expressed as two whole numbers.

Formula

The aspect ratio is the relationship between width and height, written as two numbers separated by a colon, e.g., 16:9. To get the simplified ratio, you divide both the width and the height by their greatest common divisor (GCD).

In symbols:

Ratio = (W / g) : (H / g)

where:

• W = width in any unit (pixels, mm, inches)
• H = height in the same unit
• g = greatest common divisor of W and H

For example, a 1920×1080 image has a GCD of 120. Dividing both numbers by 120 gives 16 and 9, so the ratio is 16:9.

Worked Example

Using the default values from the calculator (width = 1920 px, height = 1080 px):

1. Find the GCD of 1920 and 1080. The factors are: 1920 = 2^7 × 3 × 5; 1080 = 2^3 × 3^3 × 5. The common part is 2^3 × 3 × 5 = 120.
2. Divide width by GCD: 1920 ÷ 120 = 16.
3. Divide height by GCD: 1080 ÷ 120 = 9.
4. Write as ratio: 16:9.

The calculator shows the ratio as 16:9 and the GCD as 120.

When to Use an Aspect Ratio Calculator

You need this calculator any time you want to know whether a screen, photo, or video will fit a certain frame without distortion. Common situations:

• Choosing a new monitor or TV – you want to know if it’s 16:9, 21:9, or 4:3.
• Cropping an image for social media – each platform has preferred ratios (e.g., 1:1 for profile pictures, 4:5 for portrait posts).
• Scaling a design from one size to another – if you know the target width, you can find the matching height to keep the same shape.
• Checking whether a video file is standard widescreen or an old 4:3 format.

Note that the calculator gives the simplified ratio, not the decimal value. A ratio of 16:9 is the same as 1.777…:1, but the whole-number form is what people use in practice.

How to Read the Result

The first output is the ratio in the form W:H after simplification. For example:

• 1920×1080 → 16:9 (standard widescreen)
• 3840×2160 → 16:9 (4K UHD)
• 1080×1080 → 1:1 (square)
• 1440×1080 → 4:3 (classic monitor)
• 2560×1080 → 21:9 (ultrawide)

The second output is the GCD, which is useful if you want to verify the simplification. If the GCD is 1, the ratio is already in simplest form (e.g., 1920×1080 would not have a GCD of 1, but a 1920×1081 image would give 1920:1081).

Remember that the ratio does not tell you the actual size – only the shape. A 10-inch 16:9 screen and a 50-inch 16:9 screen have the same ratio but very different dimensions.

Common Mistakes and Misconceptions

Mistake 1: Mixing up width and height. The order matters. 16:9 is landscape, 9:16 is portrait. If you swap the numbers, you get a vertical image, which is not what most screens use.

Mistake 2: Using different units for width and height. If you measure width in pixels and height in centimeters, the ratio will be meaningless. Always use the same unit for both.

Mistake 3: Confusing aspect ratio with resolution. Aspect ratio is the shape; resolution is the total pixel count. A 1920×1080 and a 3840×2160 image both have a 16:9 ratio, but they have different resolutions.

Mistake 4: Thinking that a decimal ratio is better. Some people write 1.5:1 instead of 3:2. Both are correct, but the whole-number form is standard because it’s easier to recognize and compare.

Mistake 5: Assuming all 16:9 screens have the same diagonal. The ratio only defines the shape, not the size. A 24-inch and a 32-inch monitor can both be 16:9.

Limits of the Formula

The formula works for any pair of positive numbers, but there are a few practical limits:

• If the width or height is not an integer, the GCD concept still works mathematically, but the result may be a decimal ratio. Most real-world uses involve integers (pixels, millimeters).
• For very large numbers (e.g., 8000×4500), the GCD might be large, but the calculator handles it fine.
• The calculator does not account for pixel aspect ratio (PAR) – only the storage aspect ratio. Some video formats use non-square pixels, so the displayed shape may differ from the stored dimensions.
• For screens, the physical aspect ratio can be slightly different from the resolution ratio due to bezels or rounded corners, but in practice the resolution ratio is what matters.

If you need to scale an image to a target width while keeping the ratio, you can use the ratio to compute the missing height: new height = (target width × original height) / original width. The same works in reverse.

Frequently Asked Questions

What is the difference between 16:9 and 4:3?

16:9 is the standard widescreen format for modern TVs, monitors, and videos. 4:3 is the older, nearly square format used by CRT monitors and early television. 16:9 is wider, so it shows more horizontal content, while 4:3 shows more vertical content relative to its width.

How do I find the aspect ratio of an image without a calculator?

Divide the width by the height to get a decimal, then simplify the fraction. For example, 1920÷1080 = 1.777…, which is 16/9. Or, find the greatest common divisor of the two numbers and divide both by it.

Is 1920×1080 the same as 16:9?

Yes. 1920 and 1080 share a GCD of 120, so dividing both gives 16 and 9. Any resolution that simplifies to 16:9 – like 1280×720, 2560×1440, or 3840×2160 – is also 16:9.

What is the aspect ratio of a standard photo print?

Common print sizes have different ratios: 4×6 inches is 2:3, 5×7 inches is 5:7, and 8×10 inches is 4:5. If you crop a 16:9 image to 4×6, you will lose some of the sides.

Can I use this calculator for video editing?

Yes. Video resolutions like 1920×1080 (16:9), 1280×720 (16:9), and 720×480 (3:2 in square pixels) are common. The calculator helps you set the correct crop or scale to avoid stretching.

What does 21:9 mean?

21:9 is an ultrawide aspect ratio used for cinematic monitors and movies. It is approximately 2.33:1, which is wider than 16:9. It gives a more immersive field of view for games and films.

Related

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• 1080p Video File Size Calculator
• Bytes Calculator

in w | Width | px | 1920 | 1
in h | Height | px | 1080 | 1
out ratio | Aspect ratio | - | (w / gcd(w,h)) + ":" + (h / gcd(w,h)) | 0
out gcd | GCD | - | gcd(w,h) | 0