Free Ratio Calculator

Worked example

To reduce a screen size, stay on "Simplify" and type 1920:1080 into "Ratio". The result under "Simplified ratio" is 16 : 9, with the line "64% / 36% = 16/25 · 9/25 of the whole" under it, and nine "Equivalent ratios" from 32:18 up to 160:90. To split a total, choose "Split a total", pick the "Coffee 1:16" shortcut (ratio 1:16, "Total to split" 500, unit g) and the "Distribution" shows Part 1 (1) = 29.41 g and Part 2 (16) = 470.59 g, with "Sum" at 500. The exact shares are 29.41176 and 470.58824, and the tool rounds them to two decimals so the rounded numbers still add up to the total.

Which settings to use, and the limits

• Pick the mode that matches your question. "Simplify" reduces a ratio to lowest terms, "Proportion" finds the one missing number in a pair of equal ratios such as 2 : 3 = 10 : x, and "Split a total" divides an amount into shares by ratio, such as 50:30:20 of 1,000. The "Try:" shortcuts (16:9, 4:3, 1:1, "Coffee 1:16", "Paint mix 1:10" and "Budget 50/30/20") fill in an example for you.
• Type the ratio in whichever way is natural. The hint under the "Ratio" box says to separate parts with a colon, comma, space, "to", "x" or "by", for example 16:9, 16 to 9, 2:3:5 or 1/3:1/2. Fractions are converted exactly, so 1/3:1/2 becomes 2 : 3. Decimals are reduced exactly too, so 1.5:3 becomes 1 : 2. You can use two or more parts, such as 2:3:5.
• For a proportion, leave exactly one box blank. The four boxes are "First term (a)", "Second term (b)", "Third term (c)" and "Fourth term (x, leave blank to solve for it)". The box you leave empty is the one that gets solved, and it does not have to be the fourth. With "Direct proportion" the tool cross-multiplies (a × x = b × c), so 2 : 3 = 10 : x gives x = 15. With "Inverse proportion" the two products stay equal (a × b = c × x), so 4 workers taking 12 days and 6 workers gives x = 8 days. The working is shown under the answer.
• Use "Split a total" for money, recipes and mixes. Enter the ratio, the "Total to split" and, if you like, a "Unit (optional)" of up to 20 characters such as kg or ml. Each share is shown to two decimals and adjusted by a cent where needed so the shares add up exactly to the total, and the "Sum" row confirms it. A part of 0 is allowed in this mode as long as the parts do not all add up to 0. "Copy all shares" puts the shares on your clipboard one per line, tab separated, which pastes into a spreadsheet as columns.
• Watch the decimal comma. When a colon or slash is in the text, a comma inside a part is read as a decimal comma, so 1,5:3 is 1.5 : 3. On an English page, a group like 1,500:750 is read as 1500 : 750, and the tool shows a note beginning "Read as 1500 : 750." when another reading is possible. To avoid any doubt, put a colon between the parts and write decimals with a dot on English pages.
• Share the exact problem with a link. Your ratio, numbers, mode and unit are kept in the part of the page address after the #, and the "Share result" button, which appears once there is an answer, copies a link to the same problem. The calculation happens in your browser: the page says "Everything is calculated in your browser — nothing is uploaded."

Common problems and how to fix them

It says "Part 2 is 0. A ratio can't be simplified with a zero part, so enter a number above 0."

"Simplify" cannot reduce a ratio that has a 0 in it, and the message names which part is zero. Replace it with a number above 0. If you only want to share a total out and one share really is zero, use "Split a total" instead, which accepts a zero part.

It says that "abc" is not a number, or "A ratio needs at least two parts, for example 2:3."

The first message quotes the first piece of text that is not a number, so look at that piece for a stray letter or symbol. Units typed with the numbers (like 16cm:9cm) also trigger it, so type digits only and put the unit in the "Unit (optional)" box in "Split a total". The second message means only one number was read, so add another part, for example 2:3.

It says "Part 2 is -3. Ratio parts can't be negative, so remove the minus sign." or "The total can't be negative. Enter 0 or more."

Ratio parts can't be negative in "Simplify" or "Split a total", and the "Total to split" must be 0 or more. The minus sign is often a stray dash, as in "5 -3". Use a colon, space or "to" between the parts. In "Proportion" negative numbers are allowed, because those four boxes are plain number fields.

The "Proportion" mode says "Leave exactly one of the four boxes blank and fill in the other three."

Either all four boxes have numbers, or two or more are empty. Clear the box you want solved and fill the other three. Because 2 : 3 = 10 : x starts with the fourth box blank, typing into it makes all four full and removes the answer, so delete what you typed there.

It says "That would need dividing by zero. Check the numbers."

The term the answer would be divided by is 0, so no value exists. For example, solving 0 : 3 = 10 : x divides by the first term. Check which number you entered as 0 and replace it. The same message appears if the result is not a finite number.

How it compares

A spreadsheet or calculator can do the same sums, but you have to remember the steps: find the greatest common divisor to simplify, cross-multiply to solve a proportion, and round each share while keeping the total exact. This tool does those steps and shows its working for proportions. It does not convert units, handle two unknowns at once, or keep a history of past problems, so for a longer calculation with several linked ratios a spreadsheet is the better place to keep your numbers. For a quick one-off answer you can share by link, this is faster.