Calculators

Calculators and unit converters

Every calculator on OpenTools. Percentages, averages, arithmetic, formulas and unit conversion, worked out in your browser as you type.

All 68 of them are listed below. Each one runs inside this tab, so nothing you open or type is uploaded — see the proof.

• Angle converterConvert an angle between radians, degrees, gradians and turns, for trigonometry, CAD drawings and code that expects radians rather than degrees.
• Area converterConvert an area between square metres, square kilometres, square centimetres, hectares, acres, square feet, square inches and square miles for land or floors.
• Average calculatorWork out the arithmetic mean of a list of numbers typed with commas, spaces or semicolons between them. The total is divided by how many values you entered.
• Basic calculatorEvaluate arithmetic with +, −, ×, ÷, %, powers, and parentheses.
• Circle calculatorCalculate area, circumference, and diameter from radius.
• Coin flipperFlip one to 100 fair coins at once and see each result listed as heads or tails. Each flip is even odds and independent of the ones before it.
• Combination calculatorWork out nCr, the number of ways to choose r items from n when order does not matter. Both are whole numbers, and r cannot be larger than n.
• Complex-number calculatorAdd, subtract, multiply, or divide a+bi coordinate pairs.
• Confidence-interval calculatorCalculate a normal-approximation mean interval from mean, deviation, n, and z.
• Cooking-unit converterConvert volume-only cooking measures without assuming ingredient density.
• Correlation calculatorCalculate Pearson correlation for two equal-length lists.
• Data-size converterConvert a file size between bytes, kilobytes, megabytes and gigabytes in powers of ten, and kibibytes, mebibytes and gibibytes in powers of two.
• Determinant calculatorCalculate a determinant for a square matrix up to 6×6.
• Dice rollerRoll one to 100 dice with two to 1,000 sides each. Every individual roll is listed and then added up for a total, so d20 and d100 sets both work.
• Distance converterConvert a length between millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles, for travel legs or drawing dimensions.
• Energy converterConvert energy between joules, kilojoules, watt-hours, kilowatt-hours, calories, kilocalories and BTU (IT), for food labels, bills and heating figures.
• Exponent calculatorRaise a base to an exponent, including negative and fractional powers such as 2 to the 8 or 9 to the 0.5. Both boxes take any finite number.
• Force converterConvert a force between newtons, kilonewtons, dynes, kilogram-force and pound-force, for load ratings, spring values and physics homework answers.
• Fraction calculatorAdd, subtract, multiply or divide two fractions written as whole-number numerators and denominators. The answer comes back reduced to its lowest terms.
• Frequency converterConvert a frequency between hertz, kilohertz, megahertz, gigahertz and revolutions per minute, for clock speeds, radio bands and motor ratings.
• Fuel-economy converterConvert fuel economy between litres per 100 km, US MPG and imperial MPG. The two gallon sizes differ, so US and imperial figures are not the same.
• GCD calculatorFind the greatest common divisor of two whole numbers, the largest value that divides both exactly. Signs are ignored, so −48 and 18 give the same 6.
• Geometry calculatorCalculate area and perimeter for a selected 2D shape.
• LCM calculatorFind the least common multiple of two whole numbers, the smallest value both divide into. Useful for adding fractions with different denominators.
• Linear-equation solverSolve ax + b = 0 for the value of x from the two coefficients. a cannot be zero, since an equation without an x term has no single value to solve for.
• Linear-regression calculatorFit the least-squares line y = intercept + slope × x.
• Logarithm calculatorWork out the logarithm of x to any base you name, whether that is base 10, base 2 or e. x must be above zero and the base positive and not equal to 1.
• Margin-of-error calculatorCalculate z × sample deviation ÷ √n with an explicit z score.
• Mass converterConvert a mass between milligrams, grams, kilograms, metric tonnes, ounces, pounds and stone, for recipe amounts, parcel weights or body weight.
• Matrix calculatorAdd, subtract, or multiply bounded numeric matrices.
• Median calculatorFind the middle value of a list of numbers. The list is sorted first, and with an even count the two central values are averaged to give the median.
• Mode calculatorFind the most frequent value in a list of numbers separated by commas or spaces. Every value tied for the top count is listed, so a two-way tie shows both.
• Number to wordsSpell a safe whole number up to 999,999,999,999 in English.
• Percentage calculatorCalculate percentages, ratios, and percentage change.
• Percentile calculatorInterpolate a requested percentile in a finite number list.
• Permutation calculatorWork out nPr, the number of ways to arrange r items chosen from n where order matters. Both must be whole numbers and r cannot be larger than n.
• Power converterConvert power between watts, kilowatts, megawatts, mechanical horsepower and BTU per hour, for appliance ratings, engines and heating output.
• Pressure converterConvert pascals and common engineering pressure units.
• Prime factorizationFactor a positive safe integer up to one trillion.
• Prime-number checkerCheck whether a whole number from 2 up to one trillion is prime. Trial division by odd divisors reports it as prime or not prime, with no factor list.
• Probability calculatorCalculate favorable outcomes divided by total outcomes.
• Proportion calculatorSolve a:b = c:x for the missing fourth value when you know the other three. Useful for scaling a recipe, a map distance or a mixing ratio up or down.
• Quadratic-equation solverSolve ax² + bx + c = 0 for both roots from the three coefficients. When the discriminant is negative the pair is given in a + bi complex form.
• Random-number generatorGenerate up to 100 random whole numbers between a minimum and a maximum you set, with both ends of the range included in the possible results.
• Ratio calculatorReduce a ratio of two whole numbers to its lowest terms, such as 12:18 down to 2:3. Handy for simplifying aspect ratios, mixes and scale drawings.
• Rectangle calculatorWork out the area, perimeter and corner-to-corner diagonal of a rectangle from its length and width. Both must be zero or above, and any unit can be used.
• Regular-polygon calculatorCalculate perimeter and area from side count and side length.
• Roman-numeral converterConvert integers 1–3999 to Roman numerals or parse canonical Roman numerals.
• Root calculatorCalculate an nth root with real-number validation.
• Rounding calculatorRound a finite number to a chosen number of decimal places.
• Sample-size calculatorEstimate a proportion sample size z²p(1−p)/e² before finite-population correction.
• Scientific calculatorApply a common scientific function with explicit degrees or radians.
• Scientific-notation converterShow a finite number in normalized scientific notation.
• Sequence generatorGenerate an arithmetic sequence from a starting value, a step and a term count of up to 1,000. The step can be negative or a decimal to count down.
• Significant-figures calculatorRound a finite non-zero number to 1–100 significant figures.
• Speed converterConvert a speed between metres per second, kilometres per hour, miles per hour, knots and feet per second, for travel, running or wind figures.
• Standard-deviation calculatorWork out the population standard deviation of a list of numbers: the square root of a variance that divides the squared spread by n, not by n − 1.
• Surface-area calculatorCalculate total surface area for common closed solids.
• System-of-equations solverSolve a 2×2 linear system a₁x+b₁y=c₁ and a₂x+b₂y=c₂.
• Temperature converterConvert a temperature between Celsius, Fahrenheit and Kelvin. Values below absolute zero are rejected rather than converted into a negative Kelvin.
• Time-unit converterConvert a duration between milliseconds, seconds, minutes, hours, days and weeks, for timeouts, run times and other elapsed spans given in the wrong unit.
• Torque converterConvert torque between newton-metres, newton-centimetres, kilogram-force metres, pound-force feet and pound-force inches, for tightening specs.
• Triangle calculatorCalculate area from base and perpendicular height.
• Variance calculatorWork out the population variance of a list of numbers: each value’s squared distance from the mean, averaged over every value, not over n − 1.
• Volume calculatorCalculate common solid volumes from explicit dimensions.
• Volume converterConvert a volume between millilitres, litres, cubic metres, cubic centimetres, US fluid ounces, US cups, US gallons and cubic feet for tanks or drinks.
• Words to numberParse supported English whole-number words up to billions.
• Z-score calculatorCalculate (value − mean) ÷ population standard deviation.