Ratio Calculator

Simplify A:B. Round each input to at most 6 decimal places. Scale the rounded values to integers. Divide both integers by their greatest common divisor, and show that reduced ratio. Also show the decimal A / B to 6 decimal places. On this mode only, show A's share of A+B as a percent. If a value was rounded to 6 decimal places, say so.

Equivalent ratios. Simplify first, then multiply both parts by the same positive whole number. The result lists 2×, 3×, 4×, 5×, and 10×. A scale factor, when you enter one, adds that multiple too.

Solve a proportion. A:B = C:D means A/B = C/D. Fill the one missing value with A = B × C / D, B = A × D / C, C = A × D / B, or D = B × C / A.

The calculator accepts unitless positive numbers only. Zero, negative numbers, and non-numeric input are rejected. Division by zero returns no result.

A ratio compares two quantities. 12:18 means 12 parts of the first quantity for every 18 of the second. Order matters: 12:18 is not the same comparison as 18:12.

This page is for unitless numbers. Tooth counts, RPM, and torque belong on the gear ratio calculator. Pixel width and height belong on the aspect ratio calculator.

Divide both numbers by their greatest common divisor. For 12 and 18, that divisor is 6, so 12:18 = 2:3.

Enter A and B. Both are required. The result is the reduced ratio A:B, the decimal A / B to 6 decimal places, and A's share of A+B as a percent.

That share is A / (A + B). It belongs to Simplify a ratio only. It is not a percentage calculator.

If an input was rounded to 6 decimal places, the result says so. If neither input was rounded, that line is omitted.

Multiply both parts of a simplified ratio by the same positive whole number. 3:4 times 2 is 6:8. Times 5 is 15:20. Each of those pairs is the same comparison.

The equivalent-ratios mode simplifies first, then shows 2×, 3×, 4×, 5×, and 10×. Type a scale factor when you want a multiple that is not in that list.

A proportion is A:B = C:D, which means A/B = C/D. Enter positive numbers in three of the four boxes and leave exactly one blank.

For 2:5 = x:20, the missing value is x = 2 × 20 / 5 = 8, so 2:5 = 8:20.

The missing value is A = B × C / D, B = A × D / C, C = A × D / B, or D = B × C / A. The result shows that value and the completed proportion.

If the blank count is not exactly one, there is no result. Zero, negative numbers, and non-numeric input are rejected. Division by zero returns no result.

2:3 is a comparison of two parts. The fraction 2/3 is the first part divided by the second, which is the decimal this calculator prints as A/B.

A's share of the total is a different fraction: 2 / (2 + 3) = 2/5 = 40%. That percent appears only in Simplify a ratio.

Decimals are allowed. 1.5:2.5 is scaled to the integers 15 and 25, then divided by 5, which gives 3:5.

Each input is rounded to at most 6 decimal places before that scaling. A longer decimal is labeled as rounded.