Free Online Calculators and Converters

Popular online calculators

• Percentage CalculatorPercentage calculator for percent change, percentage difference, X% of Y and what percent one number is of another, with the formula behind each mode.
• Compound Interest CalculatorCompound interest calculator for the final balance, interest earned and effective rate over any term, compounding frequency and regular deposits or withdrawals.
• Hours CalculatorFind how many hours and minutes lie between a start and end time, or between two dates, minus any break. Results come as hh:mm, decimal hours and minutes.
• Age CalculatorFind out how old you are from a date of birth or a birth year. Get your exact age in years, months, weeks and days, plus a running age and year-of-birth lookup.
• Days CalculatorCount the days between two dates, with weekdays, weeks and months, or add days to a date to get the new date and weekday. Past and future dates both work.
• BMI CalculatorBMI calculator for adults: enter height and weight in US or metric units to get your body mass index, WHO category, BMI Prime and mortality hazard ratios.
• Water Intake CalculatorFind your daily water target and the part of it that should come from drinks, based on your age, size, activity level, pregnancy or breastfeeding status.
• Area CalculatorFind the area of a square, rectangle, triangle, circle, parallelogram, trapezoid, ellipse, sector or octagon, in mixed units, with every formula explained.
• Volume CalculatorCalculate the volume of a box, cube, cylinder, cone, sphere or triangular prism. Enter sizes in mixed units and read the result in the cubic unit you choose.
• Grade CalculatorTurn an exam score into a percentage and letter grade, find your weighted course grade with a final-exam goal, or see how one grade moves your average.
• Sleep CalculatorSleep calculator that finds a bedtime or wake-up time from 90-minute sleep cycles, your age group and time to fall asleep, with a cycle table by age.
• Discount CalculatorFind the sale price and savings for percent-off, fixed-amount, 2-for-1 and 3-for-2 deals, or the percentage discount between an original and a sale price.

Popular online converters

• Roman Numerals ConverterConvert numbers to Roman numerals and Roman numerals to numbers as you type. Includes the symbol values, the subtractive rules, worked examples and a chart.
• Data Units ConverterConvert between bits, bytes, KB to EB, binary KiB to EiB and transfer rates such as Mbps and MB/s. Choose decimal (SI) or binary counting, with tables.
• Length ConverterConvert between 13 units of length, from nanometers to leagues, including inches, feet, yards, miles and nautical miles. Exact factors and a table.
• Area ConverterConvert area between square kilometers, meters, feet, yards, inches, miles, acres, hectares and ares. Instant answers, exact factors and a reference table.
• Volume ConverterConvert volume between cubic meters, liters, gallons, quarts, pints, cups, fluid ounces and spoons. Covers US and imperial units, with tables and examples.
• Speed ConverterConvert speed between km/h, mph, meters per second, feet per second, yards per second and knots. Exact factors, worked examples and quick reference tables.
• Time Zone ConverterConvert a date and time from one time zone to another with daylight saving taken into account. Includes US and world zone tables, DST dates and examples.
• 24-hour to 12-hour ConverterConvert 24 hour time to 12 hour time with AM or PM, or go the other way. Includes the conversion rules, worked examples and a full 24 hour clock chart.

Browse by category

Online calculators by category

• Math & Geometry18 calculators
• Finance & Business14 calculators
• Health & Fitness11 calculators
• Date & Time8 calculators
• Home & Cooking6 calculators
• Everyday6 calculators

Online converters by category

• Units & Numbers7 converters
• Date & Time5 converters
• Cooking3 converters

Random generators

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• No sign-up

  Open a tool and use it. No account, no email, no paywall.

• Runs in your browser

  The math happens on your device and the numbers you type are never uploaded. Results are kept in the page address, so share a link only if you are happy to share the values.

• Formulas shown

  Most tools explain the formula behind their result and show a worked example, and each tool states its assumptions and limits, so you can check an answer rather than just trust it.