Math calculators
Percentages, fractions, and everyday math made quick.
Most everyday sums are not hard — they are just easy to get wrong in your head or on a phone keypad. The calculators below show the working, so you can see where the number came from instead of just trusting it.
Percentages and everyday numbers
Percentage calculator
Find a percentage of a number, work out what percent one value is of another, or measure the change between two numbers.
Percent change calculator
Measure the percentage increase or decrease between an original value and a new value.
Fraction calculator
Add, subtract, multiply, or divide two fractions and get the simplified result, its decimal, and the mixed-number form.
Rounding calculator
Round any number to a set number of decimal places or to the nearest 1, 10, 100 or 1000.
Statistics calculator
Paste a list of numbers and get the count, sum, mean, median, mode, range, variance, and standard deviation instantly.
School and grades
Geometry, units, and number systems
Geometry calculator
Calculate area, perimeter, circumference, and diagonals for common shapes using standard formulas.
Square footage calculator
Work out the area of a rectangular space from its length and width, in square meters, feet or yards.
Unit converter
Convert between length, mass, and temperature units with exact factors and live results.
Roman numerals converter
Convert numbers to Roman numerals and Roman numerals back to numbers, both ways, instantly.
Prime number calculator
Check whether a number is prime, factorize it into primes, or list every prime up to a limit.
General calculators
Percentage is three different questions
What people call "doing percentages" covers at least three things: what is 20% of 450, what percentage of 450 is 90, and what is the change from 450 to 540. Each has its own sum, and they get mixed up constantly. The biggest trap is the last one: a 20% rise followed by a 20% fall does not return you to the start, because the two percentages are taken from different numbers.
Percentage calculator handles the ordinary questions, while Percent change calculator is the one for when something has moved from one figure to another.
Rounding is not one rule
What happens to a number ending in exactly 5 depends on the rule you apply. Ordinary rounding goes up; other methods round to the nearest even number to avoid a systematic bias when many rounded values are added together. Rounding calculator shows which rule produced the result rather than handing you a bare number.
Area, units, and numbers
Square footage calculator turns measurements into an area and is the starting point for most home and building jobs. Geometry calculator covers the classic shapes, Unit converter moves between units of measure, and Fraction calculator works in fractions without detouring through decimals.
For heavier work there is Scientific calculator and Statistics calculator, and for numbers in their own right, Prime number calculator and Roman numerals converter.
Grades
Final grade calculator answers what you need on the last assessment to land on a target average, and GPA calculator works out a weighted grade point average. Grading scales differ by country — the calculators work on the numbers you enter and do not translate between scales.
FAQ
- Why doesn't a 20% rise then a 20% fall get me back to where I started?
- Because the two percentages are taken from different numbers. 100 plus 20% is 120, but 20% of 120 is 24, not 20. You end on 96. The bigger the percentage, the bigger the gap.
- What is the difference between percent and percentage points?
- Percentage points are the absolute difference between two percentages; percent is the relative one. A rate going from 2% to 3% has risen by 1 percentage point — but by 50%. Both are true, and the two get used interchangeably to make a change sound bigger or smaller.
- How do these calculators round?
- The rounding calculator lets you pick the rule and tells you which one it used. The others round the displayed result to a readable number of decimals but carry the full value internally, so rounding does not accumulate through the working.
- Can I work in fractions without converting to decimals?
- Yes. The fraction calculator adds, subtracts, multiplies, and divides fractions and reduces the result. That matters when the answer needs to stay a fraction — going via decimals introduces a rounding error, staying in fractions does not.
- Which scale does the GPA calculator use?
- The US 4.0 scale with credit weighting. It does not convert from other national grading systems — you enter the grades and weights you want it to work on.
- Is the statistics calculator for a sample or a population?
- It does both and shows the difference. It matters because standard deviation is calculated differently for a sample than for a full population, and the wrong choice biases the result on small data sets.