Ratio Calculator — Free Online Tool

What Is Ratio Calculator?

A free online ratio calculator. Simplify any ratio to its lowest terms, scale a ratio by setting one side to a target value, and view percentage breakdowns, decimal equivalents, and common aspect ratio presets.

A ratio expresses the relationship between two quantities, showing how many times one value contains or is contained within the other. Ratios are fundamental in design (screen aspect ratios like 16:9), cooking (ingredient proportions), finance (debt-to-income ratios), and photography (print dimensions). Ratio Calculator simplifies ratios to their lowest terms, scales them to target values, and provides percentage and decimal breakdowns.

Enter two numbers to define your ratio (e.g., 16 and 9 for a 16:9 screen ratio). The tool calculates the simplified ratio by dividing both values by their GCD, showing the simplification step. If you enter 300 and 200, the GCD is 100, so the ratio simplifies to 3:2.

The scaling feature lets you set a target value for either side of the ratio. For example, if you have a 4:3 ratio and need the width to be 1200 pixels, enter 1200 as the target for the first value, and the tool calculates the matching height: 900. This is invaluable for resizing images and videos while maintaining proportions.

The percentage breakdown shows what fraction each part represents of the whole. For a 3:2 ratio, part A is 60% and part B is 40% of the total. The decimal equivalent (1.5 for 3:2) provides another way to understand the relationship. Common presets like 16:9, 4:3, 21:9, and 1:1 are available for one-click access.

Real-World Use Cases for Ratio Calculator

Scaling a 4:3 Image to a Specific Width

You have a 4:3 image that needs to be exactly 800px wide. Enter ratio 4:3, set the target width to 800. The tool calculates the matching height: 600px. The percentage view shows the image is 57.1% width to 42.9% height proportion.

Simplifying a Recipe Ingredient Ratio

A cookie recipe uses 400g flour and 100g sugar. Enter 400 and 100 to find the simplified ratio. The GCD is 100, so the ratio simplifies to 4:1 flour to sugar. The percentage breakdown shows 80% flour to 20% sugar by weight.

Calculating a 16:9 Aspect Ratio for Video Export

You shot a video at 1920x1080 and want to confirm it is 16:9. Enter 1920 and 1080. The simplified ratio is 16:9. If you need to export at 1280px wide, set the target width to 1280, and the matching height is 720px.

Why Use Ratio Calculator?

Ratio simplification with GCD display
Scale to any target value on either side
Aspect ratio presets (16:9, 4:3, 21:9, etc.)
Percentage and decimal breakdowns

How to Use Ratio Calculator — Step by Step

Enter the two values of your ratio (e.g. 16 and 9).

View the simplified ratio and GCD.

Set a target value for either side to scale the ratio proportionally.

Use the common aspect ratio presets for quick reference.

Who Is Ratio Calculator Best For?

screen dimensions
photo cropping
recipe scaling
design layouts

Pro Tips for Ratio Calculator

1The same ratio can be written many ways (2:1, 4:2, 8:4, 200:100). Always simplify to lowest terms for clarity and comparison.
2For screen and video work, common aspect ratios are 16:9 (widescreen), 4:3 (standard), 21:9 (ultrawide), and 1:1 (square). Use the presets for one-click access.
3A ratio of 1:1 means both values are equal. A ratio of 2:1 means the first value is twice the second. Think of it as "first value per second value".
4To check if two ratios are equivalent, simplify both to lowest terms. If they match, the ratios are equivalent.

Ratio Calculator — Frequently Asked Questions

What does simplifying a ratio do?

Simplifying divides both sides by their greatest common divisor (GCD), showing the ratio in its smallest integer form.

Can I scale a ratio up?

Yes. Enter a target value for either side A or B, and the tool will calculate the matching value while preserving the ratio.

How accurate are the calculations?

All calculations use double-precision floating-point arithmetic following IEEE 754 standards. Financial calculations like loans and compound interest are verified against standard spreadsheet formulas.

Can I round results to a specific number of decimal places?

Results are typically displayed with up to 10 significant digits. You can mentally round to your desired precision for most practical use cases.

Is Ratio Calculator really free to use?

Yes, Ratio Calculator is completely free with no hidden charges, no usage limits, and no premium tiers. You can use it as often as you need without signing up or providing any personal information.

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