Online Calculators
These calculators answer the questions people type into a search box several times a day: what is 15% of 80, how many bags of concrete a slab needs, how old someone is in days, what GPA a semester of grades produces, how long a download will take or what a resistor's colour bands mean. Each one shows a worked answer as soon as the page loads, updates as you type and explains how the result was reached.
48 free tools · no sign-up · no ads
Percentages, fractions, ratios, factors, quadratic equations, long division, scientific notation and Roman numerals, each with the working shown.
Percentage Calculator
Percent of a number, percent change, and what percent one number is of anotherFraction Calculator
Add, subtract, multiply and divide fractions and mixed numbers with stepsRatio Calculator
Simplify ratios, solve for a missing value and scale ratiosGCF and LCM Calculator
Greatest common factor and least common multiple of a list of numbersPrime Factorization Calculator
Prime factors, factor tree and divisors of a number, and whether it is primeQuadratic Equation Solver
Solve ax² + bx + c = 0 with real or complex roots and stepsLong Division Calculator
Long division with every step, remainder and decimal resultScientific Notation Calculator
Convert to and from scientific and engineering notation and calculate with itRoman Numeral Converter
Convert numbers to Roman numerals and back, with validation
Solve triangles, find areas, volumes and surface areas, work out slope and line equations, and multiply or invert matrices.
Triangle Calculator
Solve any triangle from three values, including right trianglesArea Calculator
Area of rectangles, circles, triangles, trapezoids and other shapesVolume Calculator
Volume and surface area of cubes, cylinders, spheres, cones and moreSlope Calculator
Slope, angle, distance and line equation from two pointsMatrix Calculator
Add, multiply, invert and find determinants of matrices
Describe a data set, compare a value with a normal distribution, size a survey, build confidence intervals and count combinations and probabilities.
Standard Deviation Calculator
Sample and population standard deviation and variance with stepsMean, Median and Mode Calculator
Mean, median, mode, range and quartiles of a data setZ-Score Calculator
Z-scores, percentiles and normal-distribution probabilitiesConfidence Interval Calculator
Confidence intervals for a mean or a proportionSample Size Calculator
Sample size for a survey or experiment from margin of error and confidencePermutation and Combination Calculator
nPr and nCr, with and without repetitionProbability Calculator
Probability of events, unions, intersections and repeated trials
Estimate concrete, flooring, tile, roofing, landscaping materials, stairs, heating and cooling capacity and electricity costs for home projects.
Concrete Calculator
Concrete volume and bags for slabs, footings, columns and stepsSquare Footage Calculator
Square footage of rooms and irregular areas, with cost estimatesTile Calculator
Number of tiles and boxes for a floor or wall, with wasteRoofing Calculator
Roof area, pitch factor, squares and shingle bundlesGravel and Mulch Calculator
Cubic yards and tons of gravel, mulch, soil or sand for an areaStair Calculator
Riser height, tread depth and stringer length for a staircaseBTU Calculator
Heating or cooling BTUs needed for a roomElectricity Cost Calculator
Running cost of an appliance from watts, hours and price per kWh
Electronics, chemistry and physics calculators: Ohm's law, resistor codes, voltage drop, molarity, molar mass, half-life, motion and download time.
Ohm's Law Calculator
Voltage, current, resistance and power from any two valuesResistor Color Code Calculator
Resistor value and tolerance from 4, 5 or 6 color bands, and backVoltage Drop Calculator
Voltage drop in copper or aluminium wire by gauge, length and loadMolarity Calculator
Molarity, mass, volume and dilutions for solutionsMolecular Weight Calculator
Molar mass of a chemical formula with element breakdownHalf-Life Calculator
Remaining quantity, half-life or elapsed time for exponential decaySpeed, Distance and Time Calculator
Solve for speed, distance or time in any unitsDownload Time Calculator
How long a file takes to transfer at a given bandwidth
Age, time card, time sums, GPA and final grades, fuel cost, tire and shoe sizes, cooking conversions, heat index and wind chill.
Age Calculator
Exact age in years, months and days, next birthday and generationTime Card Calculator
Weekly hours from clock-in and clock-out times, with breaks and overtimeTime Calculator
Add and subtract hours, minutes and secondsGPA Calculator
Semester and cumulative GPA from grades and creditsFinal Grade Calculator
Score you need on the final exam to reach a target gradeFuel Cost Calculator
Trip fuel cost and fuel economy in MPG or L/100 kmTire Size Calculator
Compare tire sizes: diameter, sidewall and speedometer errorShoe Size Converter
Convert shoe sizes between US, UK, EU, Japan and foot lengthCooking Measurement Converter
Convert cups, grams, tablespoons and oven temperatures by ingredientHeat Index Calculator
Feels-like temperature from air temperature and humidity, plus dew pointWind Chill Calculator
Wind chill temperature and frostbite risk from temperature and wind speed
Which tool do I need?
Work out a percentage, a percent change or a discount
Pick the question in the reader's own words, such as "X is what percent of Y", and read the answer with the formula used.
Order the right amount of concrete for a slab
Enter the length, width and thickness to get cubic yards or cubic metres and the number of premixed bags, with extra for waste.
Find my exact age or the number of days until a birthday
Enter a birth date to see the age in years, months and days, the total days lived and the next birthday.
Check homework with the steps shown
Fractions, long division and quadratic equations show each step, so you can compare them with your own working.
Fraction CalculatorLong Division CalculatorQuadratic Equation Solver
Summarise a data set for a report
Paste the numbers to get the mean, median, mode and quartiles, then the standard deviation for the spread.
Mean, Median and Mode CalculatorStandard Deviation Calculator
About Calculators
They are grouped by subject. Math Calculators cover percentages, fractions, ratios, factors, quadratic equations, long division and Roman numerals. Geometry Calculators solve triangles, areas, volumes, slopes and matrices. Statistics Calculators handle standard deviation, averages, z-scores, confidence intervals, sample sizes, combinations and probability. Construction & Home estimates concrete, flooring, tile, roofing, landscaping materials, stairs, BTUs and electricity costs. Science & Electronics covers Ohm's law, resistor codes, voltage drop, chemistry and motion. Everyday Calculators handle ages, timesheets, grades, fuel, tyres, shoe sizes, cooking and the weather. Money calculators live in Personal Finance and health calculators in Health & Wellness.
Every calculation runs in your browser, so nothing you type is sent anywhere. The answers are only as good as the inputs and the model behind them: construction estimates assume typical waste and material densities you can change, statistics tools assume the conditions their formulas need (such as a roughly normal sample), and conversions such as shoe sizes follow common charts that individual brands do not always match.
Guides
- Percentages, Fractions and Ratios: How the Arithmetic Fits TogetherWhy percent change is not symmetric, how GCF and LCM drive every fraction sum, why some decimals repeat, and how prime factors explain all three.
- Mean, Median, Standard Deviation and Z-Scores ExplainedWhich average to report, why sample standard deviation divides by n - 1, why calculators disagree on quartiles, and how a z-score becomes a percentile.
- Estimating Concrete, Flooring, Tile and Gravel Without Running ShortHow to turn measurements into cubic yards, square feet, boxes and tons: the unit traps, bag yields, waste allowances and densities that decide what you actually order.
- Age, Time Cards and Time Arithmetic: How the Counting WorksWhy an exact age is counted by anniversaries, what to do with a 29 February birthday, how to turn punches into decimal payroll hours, and why 7.45 hours is not 7:45.
Frequently asked questions
Are these calculators free to use without an account?
Yes. Every calculator opens straight away with no sign-up and no ads, and the numbers you enter never leave your browser.
Do the calculators show how the answer was worked out?
Yes. Each one shows the formula it used, and the math and statistics calculators list the steps, so you can check the method as well as the result.
Where are the mortgage, loan and investment calculators?
Money calculators are in the Personal Finance category, which covers mortgages, loans, savings, retirement accounts, salaries and taxes. Business pricing calculators are in Product & Business.
How accurate are the construction and material estimates?
They are as accurate as the measurements and the assumptions. Each tool lets you change the waste allowance and material densities; check bag yields and product sizes against the supplier before you order.
Can I use these calculators on my phone?
Yes. The layouts adapt to small screens and results update as you type, so there is no separate calculate step to tap.