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Ratio calculator

Simplify two ratio parts and scale either side to a target while preserving an exact relationship.

Ratio relationship16 : 9
First 64%Second 36%

16 : 9 = 1920 : 1080

Exact scale factor × 120

Processed on your device

How it works & useful details

How it works & limits

Enter positive integer parts and a target of up to 30 digits. The ratio reduces by the greatest common divisor; the other scaled part stays a fraction when it is not an integer. Ratios, scaled values, and scale factors are exact. Share percentages are rounded approximations.

Your working space

Change the values to explore the preview. Use the action below to create a copyable, downloadable result. All calculations stay on this device; refreshing clears your work.

About this tool

Ratio calculator simplifies a two-part ratio and scales either side to a target value while keeping the exact relationship. It is useful for mixing, model scales, and resizing proportions.

Calculations use exact integer arithmetic where possible, so simplified ratios are truly reduced rather than rounded. Everything runs locally in the page.

How to use it

  1. Enter both parts of the ratio.
  2. Read the simplified form.
  3. Enter a target value for one side if you need to scale it.
  4. Check the scaled counterpart that preserves the ratio.

Worked example

A 16:9 video frame needs to be 1,080 pixels tall. Setting the second part as the target gives 1920 : 1080 with a scale factor of 120. Each part of 16 : 9 is multiplied by 120.

Ratios reduce by their greatest common divisor, so 1920 : 1080 simplifies back to 16 : 9, and 1280 : 1024 simplifies to 5 : 4. When a scaled part is not a whole number, for example 16 : 9 scaled to a height of 1,000, the tool keeps the exact fraction (16000/9 ≈ 1777.78) instead of silently rounding it.

Everyday ratio problems

  • Recipes: a 2 : 3 ratio of sugar to flour scaled to 450 g of flour needs 300 g of sugar.
  • Mixing: 1 : 4 concentrate to water for a 2.5 litre batch is 0.5 litres of concentrate.
  • Maps and models: a 1 : 25,000 map shows 1 km as 4 cm.
  • Screens and images: 4 : 3, 3 : 2, 16 : 9, and 21 : 9 aspect ratios.

The share percentages show each part's portion of the whole. For 2 : 3, that is 40% and 60%. They are rounded for display, while the ratio itself stays exact.

Frequently asked questions

How is the ratio simplified?

Both parts are divided by their greatest common divisor, so the simplified form has no common factors.

Can ratios contain decimals?

No. Parts and the target must be whole numbers of up to 30 digits. Multiply a decimal ratio first: 1.5 : 2 becomes 15 : 20, which reduces to 3 : 4.

What about ratios with zero?

A zero part is allowed if the other is not, but both zero does not describe a meaningful ratio and is rejected.