Free Calculators & Converters Tools Online
Everyday calculators and unit converters: convert length/weight/temperature/volume, calculate percentages, BMI, age, and split bills.
35 free tools · No signup · Runs in your browser
All Calculators & Converters tools
Unit Converter
Convert length, weight, temperature and volume.
Percentage Calculator
Compute percent of a number, percent change, and inverse percent.
Age Calculator
Calculate exact age in years, months and days from a birthdate.
BMI Calculator
Calculate body mass index in metric or imperial units.
Tip & Bill Splitter
Calculate tip and split a bill across any number of people.
Loan Calculator
Calculate monthly loan payments, total interest and a 12-month amortization.
Mortgage Calculator
Estimate monthly mortgage payments including taxes, insurance and HOA.
Compound Interest Calculator
See how investments grow with compounding and monthly contributions.
Simple Interest Calculator
Compute simple interest with the formula I = P × r × t.
Salary Calculator
Convert hourly to annual salary, with overtime support.
Discount Calculator
Compute sale price from a discount % or work backwards from prices.
Sales Tax Calculator
Add sales tax to a price or back out the pre-tax amount from a total.
ROI Calculator
Calculate return on investment and annualized ROI.
Markup & Margin Calculator
Convert between cost, price, markup % and margin %.
GPA Calculator
Compute weighted GPA on the standard 4.0 scale.
Grade Calculator
Compute the grade you need on the final to hit a target.
Body Fat Calculator
Estimate body fat % using the US Navy circumference method.
Calorie Calculator
BMR and TDEE via Mifflin-St Jeor with cut/maintain/bulk targets.
Macro Calculator
Convert daily calories into protein, carb and fat grams.
Pace Calculator
Solve for running pace, time or distance — in km or miles.
Pregnancy Due Date Calculator
Estimate your due date from the last menstrual period (LMP).
Fuel Economy Calculator
Convert distance and fuel into MPG, L/100km and km/L.
Ratio Calculator
Solve A:B = C:D for any single missing value.
Mean, Median, Mode Calculator
Compute mean, median, mode, range, variance and standard deviation.
Permutation & Combination Calculator
Compute nPr and nCr with arbitrary-precision BigInt.
Quadratic Equation Solver
Solve ax² + bx + c = 0 with discriminant and complex roots.
Fraction Calculator
Add, subtract, multiply or divide fractions and simplify.
Data Storage Converter
Convert between bits, bytes, KB/MB/GB and KiB/MiB/GiB.
Bandwidth Converter
Convert between bps, Kbps, Mbps, Gbps and bytes-per-second variants.
Cooking Measurement Converter
Convert cups, tbsp, tsp, ml, oz, grams and pounds for cooking.
Shoe Size Converter
Convert shoe sizes between US, UK, EU and JP for men, women and kids.
Clothing Size Converter
Convert clothing sizes between US, UK, EU and numeric for men and women.
Wind Chill Calculator
Compute apparent temperature from cold air + wind via the NWS formula.
Heat Index Calculator
Compute apparent temperature from heat + humidity (NWS Rothfusz).
Ohm's Law Calculator
Compute voltage, current, resistance and power from any two values.
About our calculators & converters tools
The calculators category brings together the everyday math that doesn't need a spreadsheet but is fiddly to do in your head. Convert kilometres to miles for a trip plan, kilograms to pounds for a recipe, Celsius to Fahrenheit for a forecast — the Unit Converter handles length, weight, temperature and volume with live two-way input, so you can type in any field and the others update instantly.
The Percentage Calculator solves the three forms most people actually need: what is X% of Y (tax, tip, discount), X is what percent of Y (commission, score), and percent change from old → new (growth, sale price). The Age Calculator returns exact years, months and days between any birthdate and reference date, plus total days, hours and minutes lived — useful for milestone planning. The BMI Calculator supports both metric and imperial input and shows the WHO classification (a useful screen, not a diagnosis). The Tip & Bill Splitter calculates tip on pre-tax or total and divides cleanly across any number of people.
All five calculators use exact international conversion factors (1 inch = 2.54 cm, 1 lb = 0.45359237 kg) and real calendar arithmetic for dates (leap years, varying month lengths). They run entirely in your browser, so they work on flaky restaurant Wi-Fi when the bill arrives.
What’s included in this category
- Unit Converter — Convert length, weight, temperature and volume.
- Percentage Calculator — Compute percent of a number, percent change, and inverse percent.
- Age Calculator — Calculate exact age in years, months and days from a birthdate.
- BMI Calculator — Calculate body mass index in metric or imperial units.
- Tip & Bill Splitter — Calculate tip and split a bill across any number of people.
- Loan Calculator — Calculate monthly loan payments, total interest and a 12-month amortization.
- Mortgage Calculator — Estimate monthly mortgage payments including taxes, insurance and HOA.
- Compound Interest Calculator — See how investments grow with compounding and monthly contributions.
- Simple Interest Calculator — Compute simple interest with the formula I = P × r × t.
- Salary Calculator — Convert hourly to annual salary, with overtime support.
- Discount Calculator — Compute sale price from a discount % or work backwards from prices.
- Sales Tax Calculator — Add sales tax to a price or back out the pre-tax amount from a total.
- ROI Calculator — Calculate return on investment and annualized ROI.
- Markup & Margin Calculator — Convert between cost, price, markup % and margin %.
- GPA Calculator — Compute weighted GPA on the standard 4.0 scale.
- Grade Calculator — Compute the grade you need on the final to hit a target.
- Body Fat Calculator — Estimate body fat % using the US Navy circumference method.
- Calorie Calculator — BMR and TDEE via Mifflin-St Jeor with cut/maintain/bulk targets.
- Macro Calculator — Convert daily calories into protein, carb and fat grams.
- Pace Calculator — Solve for running pace, time or distance — in km or miles.
- Pregnancy Due Date Calculator — Estimate your due date from the last menstrual period (LMP).
- Fuel Economy Calculator — Convert distance and fuel into MPG, L/100km and km/L.
- Ratio Calculator — Solve A:B = C:D for any single missing value.
- Mean, Median, Mode Calculator — Compute mean, median, mode, range, variance and standard deviation.
- Permutation & Combination Calculator — Compute nPr and nCr with arbitrary-precision BigInt.
- Quadratic Equation Solver — Solve ax² + bx + c = 0 with discriminant and complex roots.
- Fraction Calculator — Add, subtract, multiply or divide fractions and simplify.
- Data Storage Converter — Convert between bits, bytes, KB/MB/GB and KiB/MiB/GiB.
- Bandwidth Converter — Convert between bps, Kbps, Mbps, Gbps and bytes-per-second variants.
- Cooking Measurement Converter — Convert cups, tbsp, tsp, ml, oz, grams and pounds for cooking.
- Shoe Size Converter — Convert shoe sizes between US, UK, EU and JP for men, women and kids.
- Clothing Size Converter — Convert clothing sizes between US, UK, EU and numeric for men and women.
- Wind Chill Calculator — Compute apparent temperature from cold air + wind via the NWS formula.
- Heat Index Calculator — Compute apparent temperature from heat + humidity (NWS Rothfusz).
- Ohm's Law Calculator — Compute voltage, current, resistance and power from any two values.