Areas
Calculate the area and perimeter of squares, circles, triangles, trapezoids and ellipses.
Games to learn how to calculate
Each game takes one calculation apart: where the result comes from, where everybody gets it wrong and how to do it in your head. Four levels, eight challenges, five minutes.
183 games available right now. We publish more every week.
Mathematics
19Average
Paste your list of numbers and get the mean, median, mode, range and standard deviation.
Integrals
Compute the area under a curve between two limits using Simpson’s rule.
Derivatives
Differentiate functions symbolically and evaluate the derivative at a given point.
Powers
Raise any number to an integer, decimal or negative exponent.
Fractions
Add, subtract, multiply or divide two fractions and get the result already simplified.
GCD
Find the GCD of two or more whole numbers using Euclid’s algorithm.
LCM
Compute the LCM of several numbers to add fractions or synchronise repeating cycles.
Equations
Solve equations of the form ax + b = c and check the answer automatically.
Logarithms
Compute the logarithm in any base and read ln, log₁₀ and log₂ at the same time.
Matrices
Add, subtract and multiply matrices, and compute determinants and transposes.
Calculator
Type the whole expression and get the result instantly, brackets and functions included.
Percentage
The four most common percentage calculations in a single tool.
Pythagoras
Find the hypotenuse or a leg of a right triangle, with area and perimeter.
Quadratic equation
Solve ax² + bx + c = 0 with the discriminant, both roots and the parabola vertex.
Roots
Calculate roots of any index, including negative numbers with an odd index.
Rule of three
Solve direct and inverse proportions by entering the three known values.
Scientific
Trigonometry, logarithms, exponentials and factorials, with a degrees/radians switch.
Volume
Volume and surface area of cubes, spheres, cylinders, cones, prisms and pyramids.
Finance
16Annualised return
Turn a total gain into the equivalent annual rate so you can compare like for like.
Compound interest
How much your money grows with regular contributions, and what it is really worth once inflation…
Discount
Final price after a discount and exactly how much you save.
Inflation
What your money will be worth in a few years at a given inflation rate.
Investment
Future value of an investment and what it is really worth after inflation.
Amortisation
Payment by payment: interest and principal, and how much you save and how many months you cut by…
Loan
Monthly payment, total interest, APR with fees and insurance, and how principal and interest split…
Monthly payment
Instalment amount when the term is quoted directly in months.
Mortgage
Monthly payment, total interest and the cash you need upfront to buy a home.
Percentage increase
Apply a percentage rise to any amount and see the exact difference.
Margin
A clear distinction between margin on price and markup on cost.
ROI
Measure the percentage return of any investment or campaign.
Savings
How much you will accumulate by saving a fixed amount every month for several years.
Selling price
Set your price from the cost and the margin or markup you want to achieve.
Simple interest
Work out the interest a principal earns without reinvestment, in years, months or days.
Tip
Tip, total and split between diners in a single calculation.
Salary
5Annual salary
Convert your monthly pay into an annual figure, extra payments included.
Freelance rate
The minimum rate to hit your income target while covering costs and non-billable hours.
Hourly rate
Turn your monthly salary into the real value of every hour you work.
Overtime
What your overtime hours should pay given the uplift that applies.
Pay rise
What a raise really means, as a percentage and in money per year.
Tax
55Add VAT
Turn a tax-exclusive price into the final price your customer sees.
Argentina IVA
Add or remove Argentina IVA at the rates in force.
Australia GST
Add or remove Australia GST at the rates in force.
Austria USt
Add or remove Austria USt at the rates in force.
Belgium TVA
Add or remove Belgium TVA at the rates in force.
Bolivia IVA
Add or remove Bolivia IVA at the rates in force.
Brazil ICMS
Add or remove Brazil ICMS at the rates in force.
Bulgaria DDS
Add or remove Bulgaria DDS at the rates in force.
Canada GST/HST
Add or remove Canada GST/HST at the rates in force.
Chile IVA
Add or remove Chile IVA at the rates in force.
China VAT
Add or remove China VAT at the rates in force.
Colombia IVA
Add or remove Colombia IVA at the rates in force.
Costa Rica IVA
Add or remove Costa Rica IVA at the rates in force.
Czechia DPH
Add or remove Czechia DPH at the rates in force.
Denmark moms
Add or remove Denmark moms at the rates in force.
Ecuador IVA
Add or remove Ecuador IVA at the rates in force.
Finland ALV
Add or remove Finland ALV at the rates in force.
France TVA
Add or remove France TVA at the rates in force.
Germany MwSt
Add or remove Germany MwSt at the rates in force.
Greece FPA
Add or remove Greece FPA at the rates in force.
Guatemala IVA
Add or remove Guatemala IVA at the rates in force.
Hungary ÁFA
Add or remove Hungary ÁFA at the rates in force.
India GST
Add or remove India GST at the rates in force.
Ireland VAT
Add or remove Ireland VAT at the rates in force.
Italy IVA
Add or remove Italy IVA at the rates in force.
Japan JCT
Add or remove Japan JCT at the rates in force.
Luxembourg TVA
Add or remove Luxembourg TVA at the rates in force.
Mexico IVA
Add or remove Mexico IVA at the rates in force.
Morocco TVA
Add or remove Morocco TVA at the rates in force.
New Zealand GST
Add or remove New Zealand GST at the rates in force.
Nigeria VAT
Add or remove Nigeria VAT at the rates in force.
Norway MVA
Add or remove Norway MVA at the rates in force.
Panama ITBMS
Add or remove Panama ITBMS at the rates in force.
Paraguay IVA
Add or remove Paraguay IVA at the rates in force.
Percentage tax
Add, remove or withhold any tax expressed as a percentage.
Peru IGV
Add or remove Peru IGV at the rates in force.
Poland VAT
Add or remove Poland VAT at the rates in force.
Portugal IVA
Add or remove Portugal IVA at the rates in force.
Romania TVA
Add or remove Romania TVA at the rates in force.
Saudi Arabia VAT
Add or remove Saudi Arabia VAT at the rates in force.
Singapore GST
Add or remove Singapore GST at the rates in force.
South Africa VAT
Add or remove South Africa VAT at the rates in force.
South Korea VAT
Add or remove South Korea VAT at the rates in force.
Spain IVA
Add or remove Spain IVA at the rates in force.
Sweden moms
Add or remove Sweden moms at the rates in force.
Switzerland MWST
Add or remove Switzerland MWST at the rates in force.
the Dominican Republic ITBIS
Add or remove the Dominican Republic ITBIS at the rates in force.
the Netherlands BTW
Add or remove the Netherlands BTW at the rates in force.
the United Arab Emirates VAT
Add or remove the United Arab Emirates VAT at the rates in force.
the United Kingdom VAT
Add or remove the United Kingdom VAT at the rates in force.
the United States Sales Tax
Add or remove the United States Sales Tax at the rates in force.
Türkiye KDV
Add or remove Türkiye KDV at the rates in force.
Uruguay IVA
Add or remove Uruguay IVA at the rates in force.
VAT
Add VAT or sales tax to a net amount at whatever rate you need.
VAT included
Break a tax-inclusive price down into the net amount and the tax.
Add days
Get the resulting date after adding a period to a starting date.
Age
Work out your age in years, months, days, weeks and hours from your date of birth.
Days between dates
Count the days, weeks and months separating any two dates.
Days until
Count the days remaining (or elapsed) between today and the date you choose.
Hours worked
Work out effective working time after breaks, night shifts included.
Subtract days
Find out what date it was a given period before a reference date.
Add hours
Work with HH:MM times without tripping over base 60.
Weeks
Count the complete weeks and leftover days separating two dates.
Working days
Count business days while excluding weekends and public holidays.
Health
12BMI
Your body mass index, your WHO category, the healthy weight range for your height and the…
BMR calculator
The calories your body burns at rest, with Mifflin-St Jeor, Harris-Benedict, Katch-McArdle and…
Body fat
US Navy method estimate from your body circumferences.
Calories
The calories you need a day to lose fat, maintain or build muscle, and the split of protein, fat…
Protein
The grams of protein you need for your weight and profile: low activity, active, strength or fat…
Water intake
Recommended litres based on your weight, exercise and climate.
Due date
Estimated due date from your last period, conception, an ultrasound or IVF, with your weeks…
Heart rate zones
Your maximum heart rate and your five training zones using the Karvonen method, with the formula…
Ideal weight
Four classic formulas plus the healthy range from BMI.
Ovulation
Estimated ovulation day and fertile window from your cycle, with an adjustable luteal phase and a…
Pregnancy weeks
Gestational age in weeks and days, trimester and estimated due date.
TDEE
Your total daily calorie burn for your activity level, and the calories to lose fat or gain…
Grade needed
The minimum mark you need to reach your target for the course.
GPA
Credit-weighted grade point average with a percentage equivalent.
Grade average
Mean, median and pass count from your list of marks.
Weighted average
An average that accounts for the credits or weight of each subject.
Statistics
13Aiken’s V
Content validity from expert judge agreement, item by item.
Chi-square
Chi-square test for contingency tables and goodness of fit, with Cramér’s V, residuals, Yates’…
Cohen’s d
Effect size between two groups or before and after, with confidence intervals, plain-language…
Confidence interval
The range the true mean is likely to fall in at your chosen confidence level.
Cronbach’s alpha
Reliability of a scale or questionnaire: alpha with a confidence interval, omega, and which items…
Margin of error
How precise your survey is, given the sample you actually collected.
Pearson correlation
Pearson’s r between two variables, with p value, confidence interval, regression line and scatter…
Precision and recall
Classification metrics from a confusion matrix.
Sample size
How many responses you need to estimate a percentage or a mean, with finite population, design…
Spearman correlation
Rank correlation between two variables, which detects monotonic relationships even if they are not…
Standard deviation
Sample and population deviation, variance and coefficient of variation.
t-test
Compare two means (independent or paired) or one mean with a value, with p value, confidence…
Z score
How many standard deviations a value sits from the mean and which percentile it occupies.
Converters
17Area
Square metres, hectares, acres, square feet and more.
Celsius to Fahrenheit
Turn any temperature from the Celsius scale into Fahrenheit.
Cm to inches
Move measurements from metric to imperial in one click.
Currency
Convert between 34 currencies at today’s rate and see the inverse equivalence.
Fahrenheit to Celsius
Translate Fahrenheit temperatures into the centigrade scale.
Inches to cm
Translate screen, wheel or pipe measurements into centimetres.
Kg to pounds
Turn any weight from kilograms into pounds with the exact international factor.
Km to miles
Turn any distance from kilometres into statute miles using the official factor.
Length
Convert between metres, kilometres, miles, feet, inches and yards.
Litres to gallons
Turn volumes from litres into US gallons.
Data
Bytes, kilobytes, megabytes, gigabytes and terabytes, decimal and binary.
Metres to feet
Turn lengths and heights from metres into feet with the exact factor.
Miles to km
Translate distances in miles into the metric system with exact precision.
Pounds to kg
Convert weights in pounds into the metric system exactly.
Temperature
Convert between Celsius, Fahrenheit, Kelvin and Rankine.
Volume
Litres, millilitres, gallons, pints, cups and spoons in a single tool.
Weight
Convert between tonnes, kilos, grams, pounds, ounces and stones.
Electrical power
Active and apparent power for single and three phase installations.
Electricity use
What an appliance costs per month and per year based on hours of use.
Ohm’s law
Enter two of voltage, current or resistance and get the third.
Cars
3Average speed
The average speed of a journey in km/h, m/s and miles per hour.
Trip cost
Fuel, tolls and the split between everyone in the car.
Fuel use
Real-world consumption in litres per 100 km from a full tank fill.
Business
3Break-even
Units and revenue needed to cover every cost.
Markup and margin
Selling price from markup and its equivalent real margin.
Meeting cost
The real cost of a meeting from attendees, duration and hourly cost.
Conversion rate
The percentage of visits that turn into sales or sign-ups.
CPM
What it costs to reach a thousand impressions with your ad spend.
CTR
Percentage of clicks over impressions for ads, emails or search results.
ROAS
How much revenue each unit invested in advertising brings back.
Text
4Character count
Characters with and without spaces, lines and bytes in a text.
Reading time
How long a text takes to read, silently or aloud.
Change case
Turn text into uppercase, lowercase, title case, snake_case or camelCase.
Word count
Words, characters, sentences and paragraphs in any text.
Base64
Turn text into Base64 and recover the original text.
Colours
Convert between colour formats and check contrast against white.
Base converter
Convert numbers between bases 2, 8, 10, 16, 32 and 36.
Passwords
Random passwords with calculated entropy, generated in your browser.
Timestamp
Convert between Unix timestamps and readable UTC dates.
SEO
3Keyword density
How often your keyword appears and how much weight it carries.
Title and meta
See how your title and meta description will look in search before you publish them.
Slug generator
Turn a title into a clean URL with no accents or odd characters.
Split the bill
What everyone pays, tip included, with optional rounding.
Pomodoro
Sessions, breaks and the real time a task will take.
Savings goal
The monthly contribution needed to reach an amount within a deadline.
Token cost
What each request to a language model costs and the monthly bill, with prompt caching, reasoning…
API cost
Monthly and annual spend on an API with a fixed fee and volume pricing, to compare up to three…