Ratio Calculator
Three ways to work with ratios: reduce A : B to its lowest whole numbers, finish a proportion such as A : B = C : ?, or divide a total amount in a given ratio down to the cent.
Both terms were divided by their greatest common divisor — the ratio keeps its value and loses its common factor.
Formula and calculation
Worked example
The ratio 4 : 6 divides both terms by their greatest common divisor, 2, giving 2:3. Writing each term over the other gives 0.6667, and the same comparison at larger scales is 2:3 = 4:6 = 6:9 = 8:12.
Splitting money without losing a cent
Percentages and cents do not always divide cleanly: $100 in the ratio 1 : 2 wants $33.333… and $66.666…, and no bank works in thirds of a cent. The split mode rounds each share down to the cent — $33.33 and $66.66 — and puts the leftover cent in a Remainder row, so Part A + Part B + Remainder equals the total exactly. Decide who keeps the stray cent, or leave it in the pot. The same logic is what payroll and invoice software applies, in one form or another.
Ratios, fractions and percentages
A ratio such as 3 : 1 and the fraction 3/4 describe the same split — a ratio compares a part to a part, while a fraction compares a part to the whole. To convert, add the terms for the total: a 3 : 1 mix is 3/4 of one ingredient and 1/4 of the other, or 75% and 25%. This is the step people skip when a paint tin says 3 : 1 and they mix 3 parts to 1 part of the wrong total. Adding the terms first always tells you what the whole is.
What the results mean
- Simplified ratio
- The ratio in lowest terms: both terms divided by their greatest common divisor until no common factor is left. 4 : 6 becomes 2 : 3.
- A ÷ B
- Term A divided by Term B as a decimal — the same comparison written as a single number, useful when you need it for a formula or a spreadsheet.
- Equivalent ratios
- Ratios equal to the simplified form at two, three and four times the scale — the quick reference you want when doubling a recipe or a paint mix.
Frequently asked questions
How do I simplify a ratio?
Divide both terms by their greatest common divisor. 24 : 36 divides by 12 to give 2 : 3, and both still compare the same way. Decimals are scaled up first: 1.5 : 2 would multiply by 10 and then reduce to 3 : 4.
How do I solve a proportion like 2 : 3 = 8 : ?
Cross-multiply: 2 × ? = 3 × 8, so ? = 24 ÷ 2 = 12. The proportion is 2 : 3 = 8 : 12. Switch this calculator to “Find the missing term”, enter A, B and C, and it does the division for you.
How do I split an amount in a ratio?
Add the terms to get the number of parts, divide the total by that, then multiply back. $600 split 2 : 3 is 5 parts, so one part is $120 — giving $240 and $360. Use the split mode and any leftover cent is shown separately.
Can a ratio contain decimals or a zero?
Decimals are fine — 1.5 : 2.5 simplifies to 3 : 5. A zero term is not accepted, though: 0 : 5 has no meaningful scale, and the calculator asks for positive terms instead of returning a misleading answer.