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

Frequently asked questions

Are the unit conversion factors exact?
Yes. We use the international definitions: 1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg exactly, 1 US gallon = 3.785411784 L. Temperature uses the exact ratios (°F = °C × 9/5 + 32).
Is BMI an accurate measure of health?
BMI is a population-level proxy and ignores muscle mass, frame size and body composition. Treat it as a rough screen, not a diagnosis. Athletes often have a 'high' BMI from muscle, not fat.
Should I tip on the pre-tax or post-tax total?
By US convention, tip is calculated on the pre-tax subtotal. Many people tip on the total for simplicity, which is slightly more generous. The Tip Splitter lets you toggle between the two.
How is percent change calculated?
(new − old) / old × 100. So going from 80 to 100 is a 25% increase ((100-80)/80 × 100), and going from 100 to 80 is a 20% decrease. A negative result means a decrease.

Browse other categories