A percentage describes a quantity per hundred. It lets you compare shares even when the underlying totals differ.
The underlying idea
25% = 25/100 = 0.25. Multiply a whole by 0.25 to find one quarter of it. Divide a part by the whole and multiply by 100 to recover its percentage.
Convert between forms
25% = 25/100 = 0.25. Multiply a whole by 0.25 to find one quarter of it. Divide a part by the whole and multiply by 100 to recover its percentage. Choose measurements that describe the same object, system, or period; changing the reference changes what the result means.
Worked example
A class with 18 passes out of 24 has a 75% pass rate. A class with 30 passes out of 40 has the same rate, though the number of students differs.
Worked example
What percentage of 80 is 20?
25%
The reference whole is 80. Twenty represents one quarter of it.
Put the method into practice
- Write down the quantity you need to find.
- Identify the measurements and their units.
- Convert units before doing the calculation.
- Apply the formula and keep unrounded intermediate values.
- Check whether the result is reasonable for your situation.
Try the Percentage Calculator with your own values.
Common mistakes
Mixing units, using the wrong reference value, and rounding too early can all change the result. A calculator cannot repair inaccurate measurements. For project estimates, distinguish the calculated base quantity from allowances and supplier rounding.
What to learn next
Explore this topic’s related answers below for focused examples and alternative ways to check a result.
