Ratio Calculator
Simplify ratios of two or more terms with the greatest common divisor, split an amount in a given ratio, or find the missing value in a proportion such as a : b = c : x. Decimals handled exactly.
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About the Ratio Calculator
Ratio Calculator handles the three most common ratio jobs. Simplify reduces a ratio of two or more terms to its lowest whole-number form using the greatest common divisor and also shows it as 1 : n. Ratio split divides a total amount between parts in a given ratio. Find a missing value solves a proportion A : B = C : D when one of the four values is unknown.
Decimal ratios with up to six decimal places are converted to whole numbers exactly — for example 1.5 : 2.25 becomes 150 : 225 and then 2 : 3 — so the simplified result is exact. Terms with more decimal places are rounded to six places first, and the result is then clearly marked as approximate. In split mode, shares are rounded to 0.01 and any leftover hundredths are allocated so the shares add up exactly to the total; the currency symbol is for display only.
How to use
- Choose Simplify, Ratio split or Find a missing value.
- Enter ratio terms separated by colons or commas, for example 12 : 18 : 30.
- For a split, also enter the total amount and pick a display currency symbol.
- For a missing value, fill in three of A, B, C and D and leave the unknown empty.
- Click Calculate, then copy or download the summary.
Key features
- Exact GCD simplification for two or more terms.
- Exact handling of decimals up to six places; clearly labelled approximation beyond that.
- 1 : n form of every ratio.
- Ratio split with shares that add up exactly to the total.
- Missing-value solver for A : B = C : D using cross-multiplication.
- Method shown step by step, Copy Summary, Download Summary, Reset and Back.
Best practices
- Keep all terms in the same unit before simplifying (for example all in grams).
- Use whole numbers or short decimals when you need an exact result.
- Check the share percentages in split mode add up as expected.
- For money, remember the split is rounded to two decimal places.
- In proportion problems, make sure A and C describe the same kind of quantity.
Benefits
- Fast, exact simplification without manual factoring.
- Fair splits that always add back to the total.
- Quick answers to proportion problems.
- Private: everything runs in your browser.
Frequently asked questions
How is a ratio simplified?
Each term is divided by the greatest common divisor (GCD) of all the terms. For example GCD(12, 18, 30) = 6, so 12 : 18 : 30 simplifies to 2 : 3 : 5.
How are decimal ratios handled?
All terms are multiplied by the same power of 10 to remove decimals, then simplified exactly. 1.5 : 2.25 becomes 150 : 225 and then 2 : 3. Terms with more than six decimal places are rounded to six places first, and the result is marked as approximate.
How does Ratio split work?
Each share = total × part ÷ sum of parts. Shares are rounded to 0.01, and any leftover hundredths go to the shares with the largest remainders so the shares always add up to the total.
How is the missing value found?
A : B = C : D means A × D = B × C. For example 3 : 4 = 9 : D gives D = 4 × 9 ÷ 3 = 12.
Why can’t a term be zero or negative?
A ratio compares positive quantities. A zero or negative term makes the ratio meaningless and would cause division by zero in the calculations.
Does the currency symbol affect the split?
No. It only changes how amounts are displayed; the calculation is identical whichever symbol you choose.