Cross Multiplication Calculator
Solve proportions using cross multiplication.
Enter three values of a/b = c/d and find the unknown fourth value instantly.
Solution
Cross Multiplication solves proportions of the form a/b = c/d by multiplying diagonally:
a × d = b × c
To solve for any unknown, leave one field blank:
- Solve for a:
a = (b × c) / d - Solve for b:
b = (a × d) / c - Solve for c:
c = (a × d) / b - Solve for d:
d = (b × c) / a
Common uses:
- Scaling recipes (if 2 cups serves 4, how much for 10?)
- Map distances (1 inch = 50 miles, 3.5 inches = ?)
- Unit conversions and currency exchange
- Similar triangles in geometry