Rule of Three Online
Solve direct and inverse proportion with real-time results.

Simple Rule of Three Calculator

Calculate proportions easily with our simple rule of three calculator. Learn what it is and how to use this essential math tool.

Direct Proportion
is to
asas
is to
X
The value of X is:
--

What is Rule of Three?

Simple Rule of Three is a math method used to find an unknown value when three other values are related by proportion.

How to Use the Calculator

  • Step 1: Build the proportion in the format 'A is to B, as C is to X'.
  • Step 2: Fill Value A, Value B and Value C with the known numbers.
  • Step 3: Click Calculate to find X.
  • Step 4: Use Clear to start a new calculation.

Example: If 240 km is to 20 liters, then 30 liters is to X km. The result is X = 360 km.