Ratio Calculator
Simplify a ratio of two to six numbers, solve A : B = C : D for a missing value, scale a ratio with an equivalent-ratio table, or split a total such as 500 ml in 1 : 4 — with the working shown for each answer.
Simplify, solve, scale and split ratios.
How to use Ratio Calculator
- Pick a mode: Solve A:B = C:D, Simplify, Scale, or Split a total.
- Type your ratio terms; use Add term for ratios like 2 : 3 : 5.
- In Solve, fill three boxes and leave one blank; in Split, enter the total to share out.
- Read the answer and the worked steps, then copy it.
About Ratio Calculator
This ratio calculator has four modes. Solve finds the missing number in a proportion A : B = C : D, or checks whether four numbers you enter make a true proportion. Simplify reduces a ratio of two to six numbers to its lowest whole-number terms and shows each term's share of the total. Scale multiplies or divides every term by the same factor, or sets one term to a new value, and lists the equivalent ratios from ×1 to ×10. Split a total shares an amount such as 500 ml or $90 between the parts of a ratio, with an option for whole-number amounts that still add up to the total.
A ratio compares parts with each other. 1 : 4 means 1 part of the first thing for every 4 parts of the second, so there are 5 parts in all and the first is 1/5, or 20%, of the total, not 25%. Mixing instructions such as cleaner dilutions are often written in this part-to-part form, but some (like lab dilutions) mean 1 part in the total, so check the label. To turn a term into a share of the total, divide it by the sum of all the terms: for A : B, the first share is A ÷ (A + B). The table of common ratios under the calculator lists these shares for twelve ratios such as 1 : 2, 1 : 3 and 3 : 1, with the amounts they give from 1,000 ml and from one US gallon.
Each mode uses one short formula, and the calculator shows it with your numbers. To simplify, divide every term by their greatest common divisor (GCD): 12 : 18 has a GCD of 6, so it becomes 2 : 3. To solve a proportion, cross-multiply, because A × D = B × C whenever A : B = C : D. To scale, multiply every term by the same factor. To split a total, divide it by the sum of the parts to get one part, then multiply each part by that amount. Every calculation runs in your browser as you type, so the numbers you enter are not uploaded, and the calculator is free with no sign-up.
Frequently asked questions
- How do you calculate a ratio?
- Write the amounts in order as A : B, then divide both by their greatest common divisor (GCD) to get the simplest form. For 12 and 18 the GCD is 6, so the ratio is 12 ÷ 6 : 18 ÷ 6 = 2 : 3. Simplify mode does this for two to six numbers and shows the GCD it used.
- What is the ratio of 12 to 18, or 24 to 36?
- Both simplify to 2 : 3: divide 12 and 18 by 6, or 24 and 36 by 12. In other forms, 12 is 66.67% of 18 (12 ÷ 18), and 12 is 40% of the 30 total (12 ÷ 30), the same 2/5 share that 2 has in 2 : 3.
- How do you calculate a 3 to 1 ratio?
- Add the parts: 3 + 1 = 4 parts. One part is the total ÷ 4, so the first amount gets 3/4 (75%) of the total and the second gets 1/4 (25%). For 2 cups, one part is 0.5 cup, so the split is 1.5 cups and 0.5 cup. Split a total mode does this for any total and unit.
- How do I work out a liquid mixing ratio?
- Add the parts and treat them as shares of the finished mix. For 1 : 4 in 500 ml there are 5 parts of 100 ml each, so you use 100 ml of concentrate and 400 ml of water. If you know the amount of water instead, use Solve: 1 : 4 = x : 2000 gives x = 500 ml of concentrate for 2,000 ml of water. Check whether the label means parts of water or parts of the finished mix: 1 : 4 (1 part to 4 parts water) is weaker than 1 in 4 (1 part in every 4 of the finished mix).
- Is 1:4 the same as 1 in 4?
- No. 1 : 4 is part-to-part: 1 part to 4 parts, so 5 parts in all, and the first is 20% of the total. "1 in 4" is part-to-whole: 1 out of every 4, which is 25%. Written as a part-to-part ratio, 1 in 4 is 1 : 3.
- How do I solve for a missing value?
- In Solve mode, fill in three of the four boxes in A : B = C : D and leave exactly one blank. The calculator cross-multiplies, using A × D = B × C, and divides by the box paired with the blank one: for example D = B × C ÷ A, so 3 : 4 = 15 : D gives D = 4 × 15 ÷ 3 = 20. The working is shown under the answer. If two or more boxes are blank it tells you how many, and if the division would be by zero it names the box that is 0.
- What happens if I fill in all four boxes?
- It stops solving and checks the proportion instead. It shows A × D and B × C with your numbers and reports whether they are equal, which tells you whether the proportion is true or false. A small tolerance is applied so genuinely equal ratios like 0.1 : 0.3 = 0.2 : 0.6 are reported as true rather than failing on floating-point noise.
- How do I find equivalent ratios or scale a recipe?
- Use Scale mode. Enter the ratio, then multiply or divide every term by a factor (2 : 5 × 4 = 8 : 20), or pick Set one term to a value: for a 2 : 3 : 1 recipe when you have 7 of the first ingredient, the factor is 7 ÷ 2 = 3.5, which gives 7 : 10.5 : 3.5. A table lists the ratio multiplied by 1 to 10, with its simplest form on top when the ratio is not already in lowest terms.
- Can it simplify ratios with three or more numbers?
- Yes. Simplify, Scale and Split a total each take two to six terms; press Add term for each extra number. 6 : 9 : 15 has a GCD of 3, so it simplifies to 2 : 3 : 5, and the three terms are 20%, 30% and 50% of the total.
- Can it simplify decimals or turn a decimal into a ratio?
- Yes. Simplify mode multiplies every term by 10 until they are all whole numbers, up to nine decimal places, then divides by the GCD, so 2.5 : 5 becomes 25 : 50 and then 1 : 2. To turn a decimal into a ratio, enter it against 1: 0.75 : 1 becomes 75 : 100, which simplifies to 3 : 4. Results are rounded only for display, to at most six decimal places; the maths runs at full double precision.
- How do I convert a ratio to a percentage or fraction, or a percentage to a ratio?
- First decide what you are comparing. Each part's share of the total is a ÷ (a + b), so 2 : 3 is 2/5 = 40% and 3/5 = 60%. A as a percentage of B is a ÷ b × 100, so 2 : 3 gives 66.67%, and as a fraction A/B it is 2/3. Simplify mode shows all of these, with a dash where B is 0 because dividing by zero is undefined. Going the other way, a 25% share is 25 : 100 = 1 : 4 when compared with the whole, or 25 : 75 = 1 : 3 when compared with the rest.
- How do I get an aspect ratio from pixel dimensions?
- Use Simplify mode with the width first and the height second: 1920 and 1080 have a GCD of 120, so they reduce to 16 : 9. The Load example button fills in exactly that pair.