Free Online Calculators
26 tools, free and without ads.
This is the general-purpose set: the arithmetic that comes up often enough to be worth a dedicated page, but not often enough to remember the formula for. Percentages and discounts, the number of days between two dates, how much concrete a footing needs.
They have one thing in common beyond the maths — none of them needs to know who you are. Every calculation happens on your device, so nothing you type is transmitted, stored or logged.
Every tool in Calculators
Find a percentage of a number, what % one number is of another, and more.
Calculate a discounted sale price or a marked-up selling price instantly.
Calculate your exact age in years, months, and days.
Calculate the difference between two dates with a live countdown to future dates.
Every US federal holiday and observance for any year, with observed dates and calendar export.
A printable monthly and yearly calendar for any year, with holidays marked, ISO week numbers and your own events.
Convert times across time zones instantly. Multi-zone view with DST-aware offsets and a visual timeline.
Find sunrise, sunset, solar noon, and twilight times for any location and date.
Convert between cooking, length, weight, temperature, and volume units.
Plot your child's height, weight, and head circumference on WHO and CDC growth charts with percentile and adult height prediction.
Convert fractions to decimals and back, with millimetres alongside and the nearest 1/16, 1/32 or 1/64 mark.
Convert numbers to Roman numerals and back, with subtractive notation and input validation.
Simplify a width/height into a ratio like 16:9, or find a missing dimension from a ratio and one known side.
Convert shoe sizes between US, UK, EU, and Japan (JP), plus foot length in cm, for men, women, and kids.
Calculate running pace, time, or distance from the other two, with race presets and a splits table.
Calculate weighted GPA from courses by grade and credit hours, with +/- grades and a cumulative mode.
Find the best bedtime for a wake-up time, or wake-up times for a bedtime, based on 90-minute sleep cycles.
Calculate trip fuel cost from distance, efficiency, and price, or find your actual MPG or L/100km.
Four-function and scientific calculator with parentheses, exponents, and keyboard input.
Find what an appliance costs to run per day, month, and year from its wattage and your rate.
Estimate a due date from your last period, conception date, or a known due date, with weekly milestones.
Cubic yards and bag counts for a slab, footing, column, or flight of stairs.
Estimate gallons of paint for a room from its dimensions, doors, windows, and coats.
How many pieces fit in a sheet of plywood, fabric, or vinyl — with saw kerf, mixed rotation, and a cutting diagram.
Boxes of tile, plank, or laminate for any number of rooms — with areas left out and waste set by the lay pattern.
The AWG size a run actually needs — checked against NEC ampacity and voltage drop, with a full copper and aluminum reference table.
Which calculator do you need?
Everyday arithmetic — percentage, discount and markup, and a plain calculator for when you just want a keypad. Reach for these when the hard part is remembering which number divides which.
Dates and time — age, the difference between two dates, a full calendar, holiday dates and time zone conversion. Date arithmetic is where mental maths fails most reliably, because months are uneven and leap years are not where you expect.
Measurement and conversion — units, fractions to decimals, Roman numerals, shoe sizes and aspect ratios. These translate a number from one system into another without changing what it measures.
Project estimates — paint, concrete, flooring and tile, cut layouts and wire gauge. These take a space or a job and tell you how much to buy. They work from the dimensions you supply, so measure twice: the arithmetic is exact, but it can only be as good as the figures you feed it.
Related categories
- Financial Calculators — Money calculations — tax, tips, loan payments — with their own page.
- Health and Fitness Calculators — Body and activity estimates, which are calculations with more caveats attached.
- Craft and Sewing Calculators — Yardage and stitch maths, where the estimating gets specific to a material.