Percentage Calculations Made Clear: Change, Discounts, and Reverse Percentages
A practical guide to finding a percentage of a number, comparing two values, reversing discounts, and keeping percentage points separate from percent change.
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69 praktische tools voor tijd, klussen, natuurkunde, techniek, omrekenen, onderwijs en het dagelijks leven.
Ontdek 69 praktische tools voor datums en tijd, bouwen, natuurkunde, elektrotechniek, weer, codering, onderwijs en alledaagse taken. Schat beton, bereken je golfhandicap of controleer een toetscijfer.
Weeks Until/Since Calculator
Find weeks and days until or since a date, or calculate a date a number of weeks from today.
Months Until/Since Calculator
Count calendar months and days, or add months to today with leap-year and month-end handling.
Hours From Now Calculator
Add or subtract hours from now and see the resulting local date and time, updated live.
ISO Week Number Calculator
Look up ISO week numbers and week-years, other years and calendar weeks remaining.
Leap Year Calculator
Check Gregorian leap-year rules and find the previous and next leap years.
Life Expectancy Calculator
Reference population-average remaining life expectancy by age, sex and country. Educational statistics, not a personal prediction.
Payday Countdown Calculator
Find the next payday and count remaining yearly paydays for weekly, biweekly, semi-monthly and monthly schedules.
Playback Speed Calculator
Calculate audiobook, podcast, lecture and video listening time at any speed, with time saved and preset comparisons.
CPS Test — Clicks Per Second
Test click speed with a live counter and 1, 5, 10 or 100 second timer, then see clicks per second and an informal rating.
AdSense Revenue Calculator
Estimate monthly and annual website ad revenue from pageviews and page RPM or CPC plus CTR. Illustrative estimates, not guarantees.
Flooring Calculator
Estimate room area, waste allowance and flooring boxes in imperial or metric units for tile, laminate or hardwood.
Paint Calculator
Calculate wall area minus doors and windows, coats and paint needed in liters or US gallons.
Wallpaper Calculator
Estimate wallpaper rolls from room wall area, openings, roll dimensions and pattern waste in imperial or metric units.
Fence Calculator
Estimate fence panels and posts from perimeter length, panel width and optional gate deduction with metric or imperial units.
Sand Calculator
Estimate construction sand volume and weight with metric or imperial dimensions and waste allowance.
Topsoil Calculator
Calculate garden topsoil volume and weight in cubic yards, cubic meters, tons or tonnes.
Paver/Patio Base Calculator
Estimate construction gravel sub-base and sand bedding together using independent layer depths and metric or imperial units.
Riprap Calculator
Estimate erosion-control rock volume and weight using riprap bulk density and metric or imperial dimensions.
Hours Calculator
Calculate total hours worked between two times, with optional break deduction. Handles midnight crossover.
Time Card Calculator
Weekly timesheet calculator with daily hours, regular pay, overtime (1.5×), and gross pay breakdown.
Time Zone Calculator
Convert a date and time to multiple time zones simultaneously using accurate IANA timezone data.
Day Counter
Count days between two dates or days until/since a specific date. Inclusive or exclusive counting.
Day of the Week Calculator
Find the day of the week for any date, plus ISO week number, day number in year, and days until next occurrence.
Betoncalculator
Schat de hoeveelheid beton voor je project
Square Footage Calculator
Calculate square footage for rectangles, triangles, circles, and trapezoids. Estimate material costs.
Stair Calculator
Calculate riser height, tread depth, and stringer length. Check IRC building code compliance.
Roofing Calculator
Calculate roof area, squares, and bundles of shingles needed based on footprint and roof pitch.
Tile Calculator
Calculate tiles and boxes needed for any room. Includes waste percentage and fixture subtraction.
Mulch Calculator
Calculate cubic yards and bags of mulch needed for any garden or landscape area and depth.
Gravel Calculator
Calculate gravel volume in cubic yards and tons for different gravel types by area and depth.
Voltage Drop Calculator
Calculate voltage drop and percentage for electrical circuits. Check NEC ≤3% compliance by wire gauge.
BTU Calculator
Calculate BTU requirements for air conditioning or heating based on room size, insulation, and climate.
Electricity Calculator
Calculate electricity cost for multiple appliances. See daily, monthly, and yearly kWh usage and costs.
Ohm's Law Calculator
Solve for voltage, current, resistance, or power (V, I, R, P) given any two known electrical values.
Resistor Calculator
Convert resistor color bands to resistance value, or convert a value to its 4-band color code.
Horsepower Calculator
Convert between horsepower, kilowatts, torque, and RPM. Supports three calculation modes.
Density Calculator
Solve for density, mass, or volume using D = M/V. Supports multiple unit systems with conversions.
Speed Calculator
Solve for speed, distance, or time with S = D/T. Supports mph, km/h, m/s, knots, and more.
Molarity Calculator
Calculate molarity, moles, or volume for solutions. Outputs mol/L, mmol/L, and μmol/L.
Molecular Weight Calculator
Calculate molecular weight from a chemical formula. Shows elemental composition and mass percentages.
Wind Chill Calculator
Calculate wind chill temperature using the NWS formula. Shows frostbite risk thresholds.
Heat Index Calculator
Calculate the heat index (feels-like temperature) using the NWS Rothfusz regression formula.
Dew Point Calculator
Calculate dew point from temperature and relative humidity. Includes comfort level interpretation.
Fuel Cost Calculator
Calculate trip fuel cost from distance, MPG, and fuel price. Also shows CO₂ emissions.
Gas Mileage Calculator
Calculate MPG and L/100km from miles driven and gallons used. Estimate range and cost per mile.
IP Subnet Calculator
Calculate network address, broadcast, usable hosts, subnet mask, and wildcard from IP and CIDR.
Base64 Encoder/Decoder
Encode text to Base64 or decode Base64 strings with UTF-8 support and character count display.
URL Encoder/Decoder
Encode or decode URLs using percent-encoding. Shows which characters were encoded.
Wachtwoordgenerator
Maak veilige, cryptografisch willekeurige wachtwoorden
Bra Size Calculator
Calculate bra size in US/UK, EU, and FR/BE/ES sizing systems from underbust and bust measurements.
Height Calculator
Convert height between cm and ft+in, or predict a child's adult height using mid-parental formula.
Shoe Size Conversion
Convert shoe sizes between US, UK, EU, and CM foot length for men's and women's footwear.
Fooiencalculator
Splits de rekening en bereken eenvoudig de fooi
Love Calculator
Fun love compatibility calculator. Enter two names for a playful compatibility score — just for fun!
Dice Roller
Roll any combination of dice (d4–d100) with cryptographically fair randomness and roll history.
Golf Handicap Calculator
Calculate your World Handicap System (WHS) handicap index from up to 20 rounds of golf.
Tire Size Calculator
Decode tire size codes like 225/55R17 to get sidewall height, overall diameter, and circumference.
Eenheden omrekenen
Reken lengte, gewicht, temperatuur en meer om
Mass Calculator
Convert between all mass units: mg, g, kg, metric ton, oz, lb, stone, short ton, and long ton.
Weight Calculator
Convert weight units (kg, N, lbf, kgf) and calculate your weight on other planets and the Moon.
Roman Numeral Converter
Convert integers (1–3,999) to Roman numerals or parse Roman numeral strings back to integers.
GDP Calculator
Calculate GDP using the expenditure approach (C+I+G+NX). Includes per capita, real GDP, and growth rate.
Age Calculator
Calculate your exact age in years, months, and days from your birth date.
Date Calculator
Add or subtract days, months, and years from any date or find the difference between dates.
Time Calculator
Add, subtract, or find the difference between times in hours, minutes, and seconds.
Grade Calculator
Calculate weighted grade averages and determine your letter grade from scores.
GPA Calculator
Calculate your Grade Point Average from course grades and credit hours.
Easy Grade Calculator
Convert questions missed out of a total into a percentage, letter grade, and complete grading reference table.
Final Grade Calculator
Calculate the final exam score needed to reach a target overall grade, or project your course grade from an exam score.
Guides and explanations
Explore practical examples and the reasoning behind these calculations.
Easy Grade Calculator: Turn Questions Missed Into a Fair Percentage
A practical teacher and student guide to converting correct answers into a percentage, choosing a grading scale, handling rounding, and reading every possible quiz result.
Final Grade Calculator: Find the Exam Score You Need
Learn how to work backward from a target course grade, test whether the target is feasible, and compare possible final-exam scores without confusing a course average with an exam percentage.
CGPA to Percentage: A Careful Guide to International Grade Conversion
Understand why CGPA conversions differ by country, see transparent worked examples for common systems, and learn when an arithmetic reference is not an official credential equivalency.
How Age Calculation Works: Chronological Age, Leap Years, and Cultural Differences
Learn how exact age is calculated in years, months, and days, why leap years complicate the math, and how different cultures count age differently.
Date Math Explained: Counting Days, Adding Time, and Finding Weekdays
Master the math behind date calculations: counting days between dates, adding or subtracting time periods, business-day counting, and finding the day of the week for any date.
How to Calculate Your GPA: Weighted vs Unweighted, and How to Raise It
Learn exactly how GPA is calculated on the 4.0 scale, the difference between weighted and unweighted GPA, how credit hours factor in, and realistic strategies to raise your GPA.
Unit Conversion Guide: Metric, Imperial, and the Math That Connects Them
A practical guide to converting between metric and imperial units—length, weight, volume, and temperature—plus the dimensional analysis method that makes any conversion foolproof.
Understanding Time Zones: UTC, Daylight Saving, and Scheduling Across the Globe
How time zones work, why UTC is the universal reference, how daylight saving time shifts meetings twice a year, and practical rules for scheduling across continents.