formula is a rule or equation used to calculate the value of a quantity.

The plural of formula is formulae or formulas.

There are all types of formulae for calculating various quantities in many areas of life.


Quantity being found
Perimeter of a square
P = 4l

P = perimeter of square
l = length of square

Cost of pizzas
C = 10x + 5

C = total cost of pizzas
x = number of $10 pizzas ordered
The 5 is the $5 delivery charge

Volume of a prism
V =Al
V = volume of prism
A = area of cross-section
l = length of prism
Distance travelled
d = st
d = distance
s = speed
t = time

The subject of a formula is the term which is often on its own on the left hand side.

e.g. For the cost of pizzas formula above the subject of the formula is C

Substitution into a Formula

To find the value of a quantity in a formula we put given values into a formula in place of the variables (written as letters).

e.g. A = lw is the formula for finding the area of a rectangle.

If      l = 5 cm and w = 7 cm

A = 5 × 7 cm2

A = 35 cm2