How does the calculator simplify a ratio with decimals?

It first multiplies both sides by a power of ten until both are whole numbers, so 2.5:1.5 becomes 25:15. Then it divides both sides by their greatest common divisor, giving 5:3. The result is always the smallest pair of whole numbers with the same proportion.

How do I solve a proportion like 3:4 = 9:x?

Enter 3, 4 and 9 in their fields and leave the last one empty. The calculator cross-multiplies (3 × x = 4 × 9) and divides to get x = 12, showing each step so you can follow or check homework. Any one of the four positions can be the unknown.

What is cross-multiplication and why does it work?

In a true proportion A:B = C:D, the fractions A/B and C/D are equal, so multiplying both sides by B × D gives A × D = B × C. That turns the proportion into a simple equation with one multiplication and one division. It works for any nonzero values, including decimals.

Can I scale a recipe or mixture with this tool?

Yes — that is exactly what the Scale section is for. If a mix uses a 3:2 ratio and you need 10 units in total, it returns 6:4 instantly. You can also fix the first quantity instead, for example scaling 3:2 so the first part becomes 12, which gives 12:8.

Is anything I type sent to a server?

No. Every calculation runs locally in your browser with plain JavaScript, so nothing you enter is uploaded or stored anywhere. The page also keeps working offline once it has loaded.

Ratio Calculator

Simplify a ratio, solve a proportion for the missing value, or scale a ratio to a new total — results update as you type.

Simplify a ratio

Reduces A : B to the smallest whole numbers. Decimals are fine.

Solve a proportion

A : B = C : D — leave the unknown field empty.

Scale a ratio

Keep the proportion of A : B while changing its size.

How it works

Enter both parts of a ratio in the Simplify section to reduce it to the smallest whole numbers, even if you start with decimals.
In the Proportion section, fill three of the four fields and leave the unknown empty — the calculator solves it and shows the cross-multiplication.
Use the Scale section to grow or shrink a ratio: give a new total or a new first value and read off the full scaled pair.

Frequently asked questions

How does the calculator simplify a ratio with decimals?: It first multiplies both sides by a power of ten until both are whole numbers, so 2.5:1.5 becomes 25:15. Then it divides both sides by their greatest common divisor, giving 5:3. The result is always the smallest pair of whole numbers with the same proportion.
How do I solve a proportion like 3:4 = 9:x?: Enter 3, 4 and 9 in their fields and leave the last one empty. The calculator cross-multiplies (3 × x = 4 × 9) and divides to get x = 12, showing each step so you can follow or check homework. Any one of the four positions can be the unknown.
What is cross-multiplication and why does it work?: In a true proportion A:B = C:D, the fractions A/B and C/D are equal, so multiplying both sides by B × D gives A × D = B × C. That turns the proportion into a simple equation with one multiplication and one division. It works for any nonzero values, including decimals.
Can I scale a recipe or mixture with this tool?: Yes — that is exactly what the Scale section is for. If a mix uses a 3:2 ratio and you need 10 units in total, it returns 6:4 instantly. You can also fix the first quantity instead, for example scaling 3:2 so the first part becomes 12, which gives 12:8.
Is anything I type sent to a server?: No. Every calculation runs locally in your browser with plain JavaScript, so nothing you enter is uploaded or stored anywhere. The page also keeps working offline once it has loaded.

About this tool

This ratio calculator combines the three ratio tasks people actually need: reducing a ratio to its simplest form, solving a proportion for one unknown, and scaling a ratio up or down to a new size. Each section works independently and recalculates the moment you change a number, so there is no button to press and no page reload.

Simplification handles decimals properly. Both sides are multiplied by the same power of ten until they are whole numbers, then divided by their greatest common divisor — so 0.75:0.25 reduces cleanly to 3:1. The proportion solver uses cross-multiplication: for A:B = C:D it forms A × D = B × C, isolates the empty field, and prints the intermediate steps, which makes it useful for checking math homework rather than just copying an answer. All of this runs client-side in your browser; the numbers you type never leave your device.

Typical uses are everyday scaling problems. Cooks resize recipes from a 3:2 flour-to-water ratio to an exact batch size. Painters and concrete mixers convert mix ratios into litres or kilograms for a known total. Teachers and students verify proportion exercises step by step. Designers translate aspect ratios such as 16:9 into pixel dimensions by fixing one side and reading the other.

A few practical tips: the calculator accepts decimals and treats a comma as a decimal point, so 2,5 and 2.5 are the same. In the proportion section, leave exactly one field empty — that is how the tool knows which value to solve for. And when scaling by a new total, the total is split in the original proportion, so the two scaled parts always add back up to the number you entered.