How to use
- 1Enter the three known values.
- 2See the proportional value and copy it.
About
Calculates the simple rule of three quickly, useful for proportions in recipes, finances and studies.
How to calculate the rule of three
UtilNexo's rule of three calculator solves proportions like 'if A corresponds to B, how much does C correspond to?', ideal for recipes, scales, and conversions.
The rule of three relates two proportional quantities. If 3 items cost $15, how much do 5 cost? The calculation is 5 × 15 ÷ 3 = $25.
It is one of the most used math tools in daily life, appearing in cooking recipes, price-per-unit calculations, map scales, and dosages.
Examples
- 3, 15, 5 → 25.
- 2, 120, 3 → 180.
Limitations
- The simple rule of three assumes direct proportionality; inversely proportional quantities require a different calculation.
- The result is mathematical and does not account for real variables like taxes, progressive discounts, or losses.
How to use the rule of three calculator
- 1Enter the two known values and the third one.
- 2See the proportional value and copy it.
Frequently asked questions
How do I set up a rule of three?
Organize the values into proportional pairs and cross-multiply: the unknown is the product of the means divided by the other extreme.
Does it work for inversely proportional quantities?
The simple direct rule does not. For inverse quantities, the setup is different.
Where can I use it in daily life?
In recipes, discounts, price per kilo, scales, speeds, and many other proportion calculations.
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