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A LITTLE CLARITY. A LOT LESS MATH.
Life has questions.
Find your numbers.
From your next home project to your everyday math.
Simple, free online calculators for the things that matter.
Always free No sign-up Made for everyday life
70 handy tools7 everyday categories100% free to useYour next answer is a few clicks away
A GOOD PLACE TO START
Everyday essentials
Money & finance
Percentage Calculator
Find percentages, price discounts, and percentage changes in a few steps.
Open calculator Health & fitnessBMI Calculator
Calculate body mass index from your height and weight, with metric or imperial units.
Open calculator Money & financeMortgage / Loan Calculator
Estimate monthly loan payments, total interest, and an amortization schedule.
Open calculator Text toolsWord Counter
Count words and characters and check the length of your writing as you type.
Open calculatorTHERE’S A TOOL FOR THAT
What are you working on?
Big plans. Small questions. Start here.
THE COMPLETE TOOLBOX
Find exactly what you need.
Money & finance
Plan payments, compare percentages, and explore investment growth.
Percentage Calculator
Find percentages, price discounts, and percentage changes in a few steps.
Mortgage / Loan Calculator
Estimate monthly loan payments, total interest, and an amortization schedule.
Compound Interest Calculator
Explore how an initial investment grows with contributions and compound interest.
Tip & Bill Split Calculator
Calculate a tip, the total restaurant bill, and each person’s share when splitting the bill.
Sales Tax / VAT Calculator
Add sales tax or VAT to a net price, or extract included tax from a gross price using your chosen rate.
Hourly to Salary Calculator
Convert hourly pay into annual, monthly, and weekly gross pay with adjustable working hours and paid weeks.
Savings Goal Calculator
Find the monthly deposit needed to reach a savings target, accounting for an initial balance and assumed interest.
Simple Interest Calculator
Calculate simple interest and the final balance from principal, annual interest rate, and a term in years.
Return on Investment Calculator
Calculate investment profit and total ROI after costs, with an optional annualized comparison over your holding period.
Profit Margin & Markup Calculator
Calculate gross profit, profit margin, and markup from a selling price and cost without confusing the two percentages.
Break-Even Calculator
Estimate the sales units and revenue needed to cover fixed and variable costs for a product or service.
Health & fitness
Understand body measurements and estimate your daily energy needs.
BMI Calculator
Calculate body mass index from your height and weight, with metric or imperial units.
BMR / TDEE Calculator
Estimate basal metabolic rate and daily calorie needs using your activity level.
Body Fat Calculator
Estimate body fat percentage from body measurements using the US Navy method.
Mounjaro KwikPen Click Calculator & Dosage
Mounjaro KwikPen calculator with pen inputs, usage limitations, and an accumulation visualization.
Running Pace Calculator
Find your running pace per kilometer and mile from distance and finish time, plus average speed.
Math & everyday
From a quick conversion to geometry homework, find your next answer.
Age Calculator
Find your age in years, months, and days from a date of birth.
Unit Converter
Convert common units of length, weight, temperature, volume, area, and speed.
Area Calculator
Find the area of circles, rectangles, triangles, and other geometric shapes.
Volume Calculator
Calculate the volume of a cube, sphere, cylinder, or rectangular cuboid.
Triangle Calculator
Compute triangle sides, angles and area (Heron's formula) from various known values. Includes usage notes.
Quadratic Equation Solver
Solve ax^2 + bx + c = 0 for real or complex roots, with discriminant and step-by-step explanation.
Fraction Calculator
Add, subtract, multiply, or divide two fractions and see the simplified fraction and decimal result.
Average, Median & Range Calculator
Find the mean, median, minimum, maximum, and range of a list of numbers with a simple data summary.
Weighted Grade Calculator
Calculate a weighted course grade from assessment percentages and their weights, including partial coursework.
GPA Calculator
Calculate a credit-weighted GPA from course grade points and credits using a customizable maximum grade-point scale.
Ratio Simplifier Calculator
Simplify a two-part whole-number ratio and see how each part contributes to the total.
Random Number Generator
Generate a random whole number within an inclusive range for classroom activities, games, or everyday decisions.
Date Difference Calculator
Count calendar days and weeks between two dates, with an option to include the ending day.
Time Duration Calculator
Calculate hours and minutes between two clock times, including shifts that end after midnight and unpaid breaks.
Speed Calculator
Calculate average speed from a distance and travel time, with results in km/h, mph, and meters per second.
Fuel Cost Calculator
Estimate trip fuel use, total fuel cost, and a shared cost per traveler from distance and vehicle consumption.
Download Time Calculator
Estimate file download time from file size and connection speed, with explicit decimal and binary size units.
GCD & LCM Calculator
Find the greatest common divisor and least common multiple of two positive whole numbers.
Combinations & Permutations Calculator
Count ways to select or arrange items without replacement, with exact combination and permutation results.
Independent Event Probability Calculator
Calculate the probabilities of both, either, neither, or exactly one of two independent events.
Pythagorean Theorem Calculator
Find the hypotenuse, area, and perimeter of a right triangle from its two perpendicular sides.
Standard Deviation Calculator
Calculate population and sample standard deviation, variance, and mean from a list of numbers.
Scientific Notation Calculator
Convert a decimal number into scientific and engineering notation, with a chosen number of significant figures.
Binary, Decimal & Hex Converter
Convert a signed whole number between binary, octal, decimal, and hexadecimal with exact integer arithmetic.
Percent Error Calculator
Compare a measured value with an accepted reference and calculate absolute error, signed error, and percent error.
Electronics
Work out component values and explore the numbers behind your circuit.
Ohm's Law Calculator
Compute voltage, current, resistance and power from any two known values. Includes formulas and usage notes.
LED Resistor Calculator
Calculate the correct resistor value for your LED circuit. This tool helps you determine the appropriate series resistor value based on supply voltage and LED specifications.
SMD Resistor Calculator
Calculate SMD (Surface Mount Device) resistor values from 3-digit and 5-digit marking codes. Convert codes like '103' or '01B' to actual resistance values.
Resistor Color Code Calculator
Decode resistor color codes with our easy-to-use calculator. Determine the resistance value of 4-band and 5-band resistors instantly.
Voltage Divider Calculator
Calculate resistor values for voltage dividers. Find standard resistor combinations for your desired output voltage.
AWG Wire Size Calculator
Convert between AWG (American Wire Gauge) and metric/imperial wire sizes. Calculate wire diameter from AWG or find AWG from diameter.
RC Time Constant Calculator
Compute RC time constant (tau = R×C), with usage notes and theory on charging curve.
Reactance Calculator (Xl/Xc)
Calculate inductive (Xl) and capacitive (Xc) reactance for a given frequency, with formulas and tips.
Whip Antenna Calculator
Calculate the optimal length for quarter-wave whip antennas. This tool helps determine the correct antenna length based on frequency for radio communications and wireless projects.
Electricity Cost Calculator
Estimate appliance energy use in kWh and electricity cost from power, daily hours, days used, and your tariff.
Battery Runtime Calculator
Estimate battery runtime from voltage, amp-hour capacity, load power, and a usable-energy efficiency factor.
DC Voltage Drop Calculator
Estimate voltage drop and cable power loss in a two-wire DC circuit from current, cable length, and conductor size.
Frequency to Wavelength Calculator
Convert frequency into wavelength using the speed of light and an adjustable propagation velocity factor.
Construction
Estimate materials for flooring, walls, and concrete projects.
Flooring Calculator
Calculate flooring materials needed including wastage rates for different materials. Free flooring calculator for laminate, hardwood, tile, vinyl, and carpet.
Brick Calculator
Calculate the number of bricks needed for your wall construction project. Free online brick calculator with common brick sizes and mortar joint calculations.
Concrete / Slab Calculator
Estimate concrete volume and the number of bags needed for a rectangular slab.
Paint Calculator
Estimate paint liters and the number of cans needed from wall area, openings, coats, and product coverage.
Tile Quantity Calculator
Estimate the number of tiles and boxes required for an area, with an adjustable allowance for cuts and waste.
Gravel Calculator
Estimate gravel volume and weight from length, width, depth, and your material’s bulk density.
Mulch Calculator
Calculate mulch volume in cubic meters and liters, and estimate how many bags your garden bed needs.
Swimming Pool Volume Calculator
Estimate a rectangular pool’s water volume in cubic meters, liters, and US gallons using average depth.
Stair Riser Calculator
Estimate equal stair risers, actual riser height, and total tread run from floor rise and a target riser height.
Text tools
Count, analyze, and transform your writing in your browser.
Word Counter
Count words and characters and check the length of your writing as you type.
Unique Word Counter
Count distinct words and explore word frequency in your text.
Leetspeak Converter
Transform plain text into leetspeak with customizable character substitutions.
Reading & Speaking Time Calculator
Estimate reading and speaking duration from a word count and adjustable words-per-minute speeds.
Image tools
Turn images into data for your next microcontroller project.
Image to MCU Array Converter
Convert an image into a pixel array for microcontroller display projects.
Aspect Ratio Calculator
Simplify image dimensions into an aspect ratio and calculate a proportional height for a new width.
Pixel Density (PPI) Calculator
Calculate screen pixel density and approximate physical width and height from resolution and diagonal size.
LESS FRICTION. MORE UNDERSTANDING.
A useful answer.
And the thinking behind it.
Choose your tool, enter your numbers, and explore the result. Formula explanations and practical guidance help you understand what comes next.
Get to know CallculusMake it your calculation
Enter your values and check that you’re using the right units.
Understand your result
Use the explanation to check assumptions and compare scenarios.
A FEW MORE ANSWERS
Good to know.
Simple tools, clear expectations.
Are the calculators free to use?
Yes. All 70 calculators are free and do not require an account. Advertising helps support the site.
Can I use Callculus on my phone?
Yes. The tools work in modern mobile and desktop browsers, with no app to install.
How should I interpret my results?
Check the inputs, units, and assumptions described on each calculator page. Results depend on the formula and rounding used. Health and financial tools provide estimates; they do not replace advice tailored to your circumstances.
Can I suggest a calculator or report an issue?
Absolutely. Contact us with the tool name, your expected result, and an example that does not contain sensitive personal information.