Free Online Calculators
Enter your numbers, get the answer, and see how it was reached — plus what to do with it. Units convert as you type, and every result is a link you can send someone.
Work out how much concrete, gravel, paint or tile a job needs — and what it will cost.
- Asphalt Calculator Hot-mix asphalt in tonnes for a drive or path, from the area and compacted thickness, with the sub-base underneath.
- Ballast Calculator Ballast needed for a concrete mix, by weight, volume and bulk bags.
- Baluster Spacing Calculator How many balusters a railing run needs and the exact centre spacing, so the gap never exceeds the limit and the end gaps match.
- Block Fill Grout Calculator Grout to fill the cores of a concrete block wall, by wall area and how many cores are filled.
Size a solar array, a generator, an air conditioner or a cable run.
- Antenna Length Calculator Physical length for a dipole, vertical, loop or 5/8-wave antenna at any frequency, including the end-effect correction.
- Battery Capacity Calculator The amp-hours and watt-hours a battery bank needs to run a given load for a given time, allowing for depth of discharge and inverter losses.
- Battery Charge Time Calculator How long a battery takes to charge from a given state of charge, at a given charger current.
- Battery Runtime Calculator How long a battery will run a load, accounting for usable depth of discharge and inverter efficiency.
Fuel, charging, towing, tyres and drivetrain maths.
- 0–60 Time Calculator An empirical 0–60 mph and 0–100 km/h estimate from power and weight. Within about a second for most road cars; it is a fit to data, not a simulation.
- Air-Fuel Ratio Calculator Converts between air-fuel ratio and lambda for any fuel, and says whether a mixture is rich or lean and what that means.
- Axle Load Calculator How a vehicle’s weight and a load split between the front and rear axles, from where the load sits, checked against the axle ratings.
- Bicycle Gear Calculator Gear ratio, gear inches and development for a chainring and sprocket combination, with the speed at a chosen cadence.
Areas, volumes and running costs around the house.
- Blind and Shade Size Calculator The width and drop to order for inside- or outside-mount blinds.
- Countertop and Cabinet Run Calculator Worktop area, slabs needed and how many base cabinets fit along a run.
- Curtain Fabric Calculator The curtain fabric needed for a window, allowing for fullness, hems and pattern repeat.
- Drainage Slope and Fall Calculator The fall a drain, pipe or gutter needs over its length, as a ratio and a percentage.
Units, measures and standards.
- Angle Converter Convert between degrees, radians, gradians, turns, arcminutes and arcseconds.
- Area Converter Convert between square metres, square feet, acres, hectares and square miles.
- Data Storage Converter Convert between bits, bytes, kilobytes, megabytes, gigabytes, terabytes and their binary equivalents.
- Density Converter Convert between kg/m³, g/cm³, kg/L, lb/ft³, lb/in³ and lb/yd³.
Body composition, training and pace.
- 10K Pace Calculator The pace per km and per mile for a target 10K time, with splits for the whole race.
- 5K Pace Calculator The pace per km and per mile for a target 5K time, with splits for the whole race.
- Baby Age and Corrected Age Calculator A baby’s age in months, weeks and days, with corrected age if born before 37 weeks.
- Barbell Plate Calculator Which plates to load on each side of the bar for a target weight, in kilograms or pounds.
Motion, energy, waves and thermodynamics.
- Acceleration Calculator Acceleration from a change in speed, over a time or a distance, in m/s², ft/s² and g.
- Angular Acceleration Calculator Angular acceleration from a change in rotation rate, with the turns made and the torque needed.
- Angular Velocity and Circular Period Calculator Angular velocity in rad/s from rpm, an angle and time, a period or a speed, with the period and edge speed.
- Bernoulli Equation Calculator Solve Bernoulli’s equation for the downstream pressure or speed along a streamline.
Moles, solutions, gases and equilibria.
- Acid-Base Titration Calculator Unknown concentration or titrant volume at the equivalence point, using the coefficients of the balanced equation.
- Activation Energy Calculator Activation energy from rate constants measured at two temperatures.
- Arrhenius Equation Calculator Rate constant from activation energy and temperature, and how much it changes at a second temperature.
- Atom Economy Calculator Atom economy of a reaction from the molar masses and coefficients in its balanced equation.
Averages, spread, distributions and tests.
- Bayes’ Theorem Calculator Updates a probability when new evidence comes in.
- Binomial Distribution Calculator The chance of a given number of successes in a fixed number of independent trials.
- Birthday Paradox Calculator The chance that two people in a group share a birthday.
- Card Probability Calculator The chance of drawing a number of chosen cards from a deck, without putting them back.
Interest, loans, savings and returns. You supply the rate.
- 50/30/20 Budget Calculator Splits your take-home pay into needs, wants and savings.
- 70 Percent Rule Calculator The most to pay for a flip under the 70 percent rule.
- Amortisation Calculator A year-by-year amortisation schedule, and the balance, principal and interest paid at any point in the loan.
- Annuity Calculator Future value and present value of a series of equal payments.
Margins, break-even, SaaS and campaign metrics.
- A/B Test Significance Calculator Whether the gap between two variants is statistically significant, with p-value, uplift and the sample size to plan for.
- Billable Utilisation Calculator Billable utilisation from hours billed and hours available, and the revenue it brings at your rate.
- Burn Rate and Runway Calculator Gross burn, net burn and how many months of cash a business has left.
- CAC Payback Calculator Months to recover customer acquisition cost on a gross margin basis.
Storage, bandwidth, networking and colour.
- Aspect Ratio Calculator The aspect ratio of any width and height, and the nearest common ratio.
- Aspect Ratio Resize Calculator The new width or height that keeps an image’s shape, or the size that fits or fills a box.
- Audio Bitrate Calculator Bitrate of uncompressed audio from its sample rate and bit depth, and the average bitrate of any file.
- Audio File Size Calculator The size of an MP3, AAC or other audio file from its bitrate and length.
Seed, fertiliser, irrigation and yield.
- Animal Water Requirement Calculator Daily water for a herd or flock, the storage to hold in reserve and the flow to refill it, from your own per-head figure.
- Compost C:N Ratio Calculator The carbon to nitrogen ratio and moisture of a compost mix, and how much of a material brings it to your target.
- Crop Yield Estimate Calculator Estimate grain yield before harvest from heads per square metre, grains per head and thousand grain weight.
- Drip Irrigation Flow Calculator Total flow, application rate and run time for a drip system, from emitter flow and spacing.
Scaling, conversion, timing and costing.
- ABV from Gravity Calculator The alcohol content of finished homebrew beer, cider, wine or mead, from hydrometer readings.
- Baker’s Percentage Calculator Turn a dough recipe into baker’s percentages, with every ingredient as a share of the flour.
- Bread Recipe Scaling Calculator Scale a bread recipe to any number of loaves, using the total dough you need.
- Brine Ratio Calculator How much salt and sugar to add to water for an ordinary kitchen brine, by percentage.
Grades, GPA and study planning.
- Assignment Weight Calculator What share of your course an assignment is worth, and how its score moves your grade.
- Attendance Percentage and Required Attendance Calculator Your attendance percentage, how many classes you need to reach a required level, and how many you can miss.
- CGPA to Percentage and Percentage to CGPA Calculator Convert between CGPA and percentage with CBSE’s 9.5 factor, or with your own institution’s multiplier.
- Class Rank and Percentile from Rank Calculator Turn a class rank into a percentile and a top-percent figure, with the method stated.
Ages, durations, working days and deadlines.
- Add or Subtract Days, Weeks, Months and Years From a Date Find the date a number of days, weeks, months or years before or after another date.
- Age Calculator Exact age in years, months and days, in total days, and on any date you choose.
- Birthday Countdown Calculator How many days until your next birthday, the day it falls on and the age you will turn.
- Business Days and Working Days Calculator Count the weekdays between two dates, leaving out weekends and any public holidays you enter.
Scoring, pace, odds and game maths.
- Attempts for a Given Chance Calculator How many attempts give a chosen chance of getting a drop at least once.
- Baseball ERA Calculator Earned run average from earned runs and innings pitched.
- Baseball OPS, Slugging and Batting Average Calculator On-base plus slugging, with slugging percentage, on-base percentage and batting average, from a batting line.
- Baseball WHIP Calculator Walks plus hits per inning pitched.
Distance, bearing, daylight and trip costs.
- Area Density Calculator Mass per unit area in kg/m², g/m², lb/ft² and oz/yd², from a mass and an area.
- Bearing Between Coordinates Calculator The initial and final bearing between two latitude and longitude points, with the compass point and the constant-compass bearing.
- Coordinate Converter: DMS and Decimal Degrees Converts latitude and longitude between decimal degrees, degrees minutes seconds, and degrees decimal minutes.
- Daylight Hours Calculator The length of the day for any date, latitude and longitude, with how it changes through the year.