Numbers, solved
Math
Percentages, ratios, fractions and statistics with exact arithmetic. Every tool shows its formula so you can check the work yourself.
Percentage Calculator
Three percentage questions in one tool: P% of X, X is what % of Y, X is P% of what.
Percentage Change Calculator
Measure increase or decrease between two values as a signed percentage.
Ratio Calculator
Simplify any ratio to smallest whole-number terms, with decimal value and share of total.
Fraction Calculator
Add, subtract, multiply and divide fractions with exact reduced answers.
Average Calculator
Mean, median, mode and range for a list of numbers — plus both standard deviations.
Standard Deviation Calculator
Sample or population standard deviation with every step shown: the mean, each deviation and its square, the variance and its root.
GPA Calculator
Add your courses, grades and credit hours to see your unweighted and weighted GPA on the 4.0 scale, with the standard +0.5 honors and +1.0 AP / IB bonus applied to weighted scores.
Roman Numeral Calculator
Convert Arabic numbers to Roman numerals (1–3999) and back, validate Roman syntax, and add or subtract two Roman numerals via integer arithmetic.
What this covers
Percentages, ratios, fractions and descriptive statistics — the arithmetic that turns up in shopping, coursework, recipes, screen sizes and spreadsheets. Every tool prints the formula it used, so the working can be checked rather than trusted.
Which tool to use
Reach for the Percentage Calculator when one of the three numbers in “P% of X” is missing, and Percentage Change when you have a before and an after and want the movement between them. The Ratio Calculator reduces a pair to its smallest whole terms; the Fraction Calculator does exact arithmetic on fractions rather than on their decimals. The Average Calculator is for a list rather than a pair — mean, median, mode, spread. The Standard Deviation Calculator works that spread through step by step, from each value’s deviation to the variance and the standard error.
Frequently asked questions
Why do percentage increase and decrease not cancel out?
Because the base changes. Going from 80 to 100 is +25%, but coming back from 100 to 80 is −20%: the first is measured against 80, the second against 100. Both are correct; they are answers to different questions.
Do these tools round?
Only for display. The arithmetic runs at full precision and the rounding happens once, at the end, so repeated steps never accumulate error.
What happens with a zero denominator?
You get a clear message rather than a number. Dividing by zero has no answer, and inventing one would be worse than saying so.