Formula library
Calculator formulas
A browsable index of the formulas behind CalculTools calculators. Each formula links to a working calculator page.
Business
Profit Margin Calculator
margin = (revenue − cost) ÷ revenue × 100Calculate gross profit and profit margin percentage.Markup Calculatormarkup = (price − cost) ÷ cost × 100Calculate markup percentage from cost and selling price.Freelance Rate Calculatorrate = (target + expenses) ÷ billable hoursEstimate an hourly freelance rate from income goals and billable hours.Invoice Total Calculatortotal = subtotal − discount + taxCalculate invoice subtotal, tax, discount, and final total.PayPal Fee Calculatorfee = amount × percent ÷ 100 + fixed feeEstimate PayPal-style transaction fees using a percentage plus fixed fee.Stripe Fee Calculatorfee = amount × percent ÷ 100 + fixed feeEstimate card processing fees using a percentage plus fixed fee.ROI CalculatorROI = (gain − cost) ÷ cost × 100Calculate return on investment percentage.CPM CalculatorCPM = cost ÷ impressions × 1000Calculate advertising cost per thousand impressions.CPC CalculatorCPC = cost ÷ clicksCalculate advertising cost per click.CTR CalculatorCTR = clicks ÷ impressions × 100Calculate click-through rate from clicks and impressions.Conversion Rate Calculatorconversion rate = conversions ÷ visitors × 100Calculate conversion rate from visitors and conversions.Break-Even Calculatorbreak-even units = fixed costs ÷ (price − variable cost)Calculate how many units you need to sell to break even.Commission Calculatorcommission = sales × commission rateCalculate commission earnings from sales and commission rate.Revenue Growth Calculatorgrowth = (current − previous) ÷ previous × 100Calculate revenue growth percentage between two periods.Customer Acquisition Cost CalculatorCAC = acquisition spend ÷ new customersCalculate CAC from marketing spend and new customers.LTV CalculatorLTV = AOV × purchase frequency × lifespanEstimate customer lifetime value from average order, purchase frequency, and lifespan.Churn Rate Calculatorchurn rate = lost customers ÷ starting customers × 100Calculate customer churn rate for a period.Meeting Cost Calculatormeeting cost = people × hourly rate × minutes ÷ 60Estimate the labor cost of a meeting.Gross Profit Calculatorgross profit = revenue − COGSCalculate gross profit from revenue and cost of goods sold.Net Profit Calculatornet profit = revenue − expensesCalculate net profit after expenses.Operating Margin Calculatoroperating margin = operating income ÷ revenue × 100Calculate operating margin from operating income and revenue.ARPU CalculatorARPU = revenue ÷ usersCalculate average revenue per user.Lead Conversion Calculatorlead conversion rate = customers ÷ leads × 100Calculate how many leads convert into customers.Email Open Rate Calculatoropen rate = opens ÷ delivered × 100Calculate email campaign open rate.Email Click Rate Calculatoremail click rate = clicks ÷ delivered × 100Calculate email click rate from clicks and delivered emails.ROAS CalculatorROAS = revenue ÷ ad spendCalculate return on ad spend.Profit Per Unit Calculatorprofit per unit = selling price − unit costCalculate profit per item sold.Inventory Turnover Calculatorinventory turnover = COGS ÷ average inventoryCalculate inventory turnover from COGS and average inventory.Productivity Calculatorproductivity = output ÷ hoursCalculate output per hour or per worker.Burn Rate Calculatorburn rate = (starting cash − ending cash) ÷ monthsCalculate monthly cash burn.Runway Calculatorrunway = cash ÷ monthly burnEstimate how many months cash will last.Construction
Area Calculator
area = length × widthCalculate rectangle area from length and width.Volume Calculatorvolume = length × width × heightCalculate box volume from length, width, and height.Paint Calculatorliters = area × coats ÷ coverageEstimate paint needed from wall area and coverage.Flooring Calculatormaterial = area × (1 + waste%)Estimate flooring material needed including waste.Tile Calculatortiles = area × (1 + waste%) ÷ tile areaEstimate number of tiles needed for an area.Concrete Calculatorvolume = length × width × depthEstimate concrete volume for a slab.Room Area Calculatorarea = length × widthCalculate room floor area.Wall Area Calculatorpaintable area = width × height − openingsCalculate wall area from wall width and height.Square Footage Calculatorsquare footage = length × widthCalculate square footage from length and width in feet.Roofing Calculatorroof area = length × width × pitch factor × waste factorEstimate roofing area and number of roofing squares.Gravel Calculatorvolume ft³ = length × width × depth/12Estimate gravel volume and approximate weight.Mulch Calculatorvolume ft³ = length × width × depth/12Estimate mulch volume in cubic feet and cubic yards.Stair Calculatorriser height = total rise ÷ steps; total run = tread run × stepsEstimate stair riser height from total rise and number of steps.BTU CalculatorBTU = area × BTU factorEstimate room cooling BTU from square footage and climate factor.Converters
Unit Converter
uses standard conversion factorsConvert common length, weight, and temperature units.Length Converterfeet = meters × 3.28084Convert meters to feet, inches, kilometers, and miles.Weight Converterpounds = kg × 2.20462Convert kilograms to pounds, ounces, grams, and stones.Temperature ConverterF = C × 9/5 + 32Convert Celsius to Fahrenheit and Kelvin.Speed Convertermph = kph × 0.621371Convert kilometers per hour to miles per hour and meters per second.Date & Time
Age Calculator
age = difference between today and birth dateCalculate exact age from date of birth.Date Calculatorresult date = start date + daysAdd or subtract days from a date.Days Between Dates Calculatordays = end date − start dateCount days between two dates.Time Duration Calculatorduration = end time − start timeCalculate the duration between two times.Countdown Calculatordays remaining = target date − todayCalculate days remaining until a future date.Work Hours Calculatorwork hours = end time − start time − breakCalculate total work hours from start time, end time, and break length.Time Zone Difference Calculatordifference = to offset − from offsetCalculate the hour difference between two UTC offsets.Due Date Countdown Calculatordays left = due date − todayCalculate days remaining until a due date.Education
Grade Calculator
final contribution = score × weight ÷ 100Calculate weighted grade from score and weight.GPA CalculatorGPA = grade points ÷ creditsCalculate GPA from total grade points and credits.GPA to Percentage Calculatorpercentage ≈ GPA ÷ scale × 100Convert GPA to an approximate percentage using a simple scale.Final Grade Calculatorneeded = (target − current × (1 − final weight)) ÷ final weightCalculate the final exam score needed to reach a target course grade.Weighted Grade Calculatorweighted grade = sum(grade × weight) ÷ total weightCalculate a weighted grade from three grade/weight pairs.Engineering
Ohm’s Law Calculator
V = I × R; P = V × ICalculate voltage, current, resistance, and power using Ohm’s law.Voltage Drop Calculatorvoltage drop = 2 × length × current × resistance ÷ 1000Estimate voltage drop from current, wire resistance, and cable length.Resistor Calculatorresistance = voltage ÷ currentCalculate resistance from voltage and current.Bandwidth Calculatortime seconds = size GB × 8192 ÷ MbpsEstimate data transfer time from file size and bandwidth.Data Transfer Calculatordata GB = speed Mbps × seconds ÷ 8192Calculate data transferred from speed and time.Everyday
Fuel Cost Calculator
cost = distance × L/100km ÷ 100 × priceEstimate trip fuel cost from distance, efficiency, and fuel price.Electricity Cost Calculatorcost = watts ÷ 1000 × hours × priceEstimate electricity cost from watts, hours, and price per kWh.Pace Calculatorpace = total minutes ÷ distanceCalculate pace per kilometer from distance and time.Download Time Calculatortime seconds = file gigabits ÷ MbpsEstimate download time from file size and internet speed.Health
BMI Calculator
BMI = weight kg ÷ height m²Calculate body mass index from height and weight.Calorie CalculatorBMR × activity multiplierEstimate daily calories using the Mifflin-St Jeor equation.Pregnancy Due Date Calculatordue date = LMP + 280 daysEstimate due date from last menstrual period.Body Fat Calculatorbody fat ≈ 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4Estimate body fat percentage using a simple BMI-based method.Ideal Weight CalculatorDevine formula adjusted from 5 feet baselineEstimate ideal body weight using height.Water Intake Calculatorwater ≈ 35ml per kg + activity adjustmentEstimate daily water intake from body weight.BMR CalculatorMifflin-St Jeor BMR equationEstimate basal metabolic rate using weight, height, age, and sex.TDEE CalculatorTDEE = BMR × activity multiplierEstimate total daily energy expenditure from BMR and activity level.Macro Calculatorgrams = calories × macro % ÷ calories per gramSplit daily calories into protein, carbs, and fat targets.Protein Calculatorprotein target = weight × grams per kgEstimate daily protein target from body weight and grams per kg.Calories Burned Calculatorcalories = MET × 3.5 × weight ÷ 200 × minutesEstimate calories burned using MET, body weight, and duration.Target Heart Rate Calculatortarget zone = (220 − age) × intensityEstimate target heart rate zone from age and intensity.Sleep Calculatorwake time = bedtime + cycles × 90 minutesEstimate wake-up or bedtime options based on 90-minute sleep cycles.BMI Prime CalculatorBMI Prime = BMI ÷ 25Calculate BMI Prime relative to the upper normal BMI limit.Waist to Height Ratio Calculatorratio = waist ÷ heightCalculate waist-to-height ratio.One Rep Max Calculator1RM ≈ weight × (1 + reps ÷ 30)Estimate one-rep max from lifted weight and reps.Walking Calorie Calculatorcalories = MET × 3.5 × weight ÷ 200 × minutesEstimate calories burned while walking.Running Calorie Calculatorcalories = MET × 3.5 × weight ÷ 200 × minutesEstimate calories burned while running.Heart Rate Zone Calculatormax heart rate ≈ 220 − age; zones are percentages of maxEstimate training heart-rate zones from age.Pregnancy Week Calculatorpregnancy week = days since LMP ÷ 7Estimate pregnancy week from last menstrual period date.Ideal Body Weight CalculatorDevine estimate based on inches over 5 feetEstimate ideal body weight using height and sex.Army Body Fat Calculatorbody fat estimate using tape-measure circumference methodEstimate body fat using neck, waist, height, and sex inputs.Math
Percentage Calculator
result = value × percent ÷ 100Calculate percentages, parts, totals, increases, and decreases.Percentage Change Calculatorchange = (new − old) ÷ old × 100Find the percentage increase or decrease from an old value to a new value.Average Calculatoraverage = sum ÷ countCalculate the average of comma-separated numbers.Ratio Calculatorsimplified ratio = a/gcd : b/gcdSimplify a two-number ratio.Fraction Calculatorcalculate using common denominator or fraction operationAdd, subtract, multiply, or divide two fractions.Square Root Calculatorresult = √valueCalculate the square root of a number.Scientific Calculatorpower, root, sin, cos, tan, ln, log10Calculate powers, roots, sine, cosine, tangent, and logarithms.LCM CalculatorLCM = |a × b| ÷ GCD(a,b)Calculate least common multiple of two numbers.GCD CalculatorEuclidean algorithmCalculate greatest common divisor of two numbers.Prime Number Calculatortest divisibility up to √nCheck whether a number is prime.Circle Calculatorarea = πr², circumference = 2πrCalculate circle area and circumference from radius.Triangle Calculatorarea = base × height ÷ 2Calculate triangle area from base and height.Aspect Ratio Calculatornew height = original height × new width ÷ original widthScale width or height while preserving aspect ratio.Permutation CalculatornPr = n! ÷ (n − r)!Calculate permutations nPr.Combination CalculatornCr = n! ÷ (r! × (n − r)!)Calculate combinations nCr.Standard Deviation Calculatorstandard deviation = sqrt(sum((x − mean)^2) ÷ n)Calculate mean, variance, and standard deviation from comma-separated numbers.Statistics Calculatorsummary statistics from a number setCalculate count, sum, mean, median, min, max, and range.Mean Median Mode Calculatormean = sum ÷ count; median = middle value; mode = most frequent valueFind mean, median, and mode from a list of numbers.Probability Calculatorprobability = favorable ÷ total × 100Calculate probability from favorable outcomes and total outcomes.Quadratic Formula Calculatorx = (-b ± √(b² − 4ac)) ÷ 2aSolve ax² + bx + c = 0 using the quadratic formula.Slope Calculatorslope = (y2 − y1) ÷ (x2 − x1)Find slope from two coordinate points.Log Calculatorlog base b of x = ln(x) ÷ ln(b)Calculate logarithm for a value and base.Pythagorean Theorem Calculatorc = √(a² + b²)Calculate the hypotenuse from two right-triangle legs.Long Division Calculatordividend = divisor × quotient + remainderCalculate quotient and remainder for integer division.Number to Percent Calculatorpercent = number × 100Convert a number or decimal into a percent.Percent to Decimal Calculatordecimal = percent ÷ 100Convert a percent into decimal form.Decimal to Fraction Calculatorfraction ≈ decimal × denominator ÷ denominatorConvert a decimal to an approximate fraction.Fraction to Decimal Calculatordecimal = numerator ÷ denominatorConvert a fraction into decimal and percent form.Rounding Calculatorrounded value = number rounded to selected placesRound a number to a selected number of decimal places.Absolute Value Calculatorabsolute value = distance from zeroCalculate the absolute value of a number.Factorial Calculatorn! = n × (n−1) × ... × 1Calculate n factorial for non-negative integers.Modulo Calculatormodulo = remainder after dividend ÷ divisorCalculate the remainder after division.Linear Equation Calculatorx = (c − b) ÷ aSolve a simple linear equation ax + b = c.Distance Between Points Calculatordistance = √((x2−x1)² + (y2−y1)²)Calculate distance between two coordinate points.Midpoint Calculatormidpoint = ((x1+x2)/2, (y1+y2)/2)Find the midpoint between two coordinate points.Money
Discount Calculator
sale price = price × (1 − discount ÷ 100)Calculate sale price and money saved after a discount.VAT CalculatorVAT = amount × rate ÷ 100Add or remove VAT from a price.Sales Tax Calculatortax = amount × rate ÷ 100Calculate sales tax and total price after tax.Tip Calculatortip = bill × tip% ÷ 100Calculate tip amount, total bill, and split per person.Loan Calculatormonthly payment = P × r(1+r)^n ÷ ((1+r)^n − 1)Estimate monthly loan payment, total repayment, and interest.Mortgage Calculatorpayment = P × r(1+r)^n ÷ ((1+r)^n − 1)Estimate monthly mortgage payment before taxes and insurance.Simple Interest Calculatorinterest = principal × rate × timeCalculate simple interest over time.Compound Interest CalculatorA = P(1 + r/n)^(nt)Calculate compound interest growth with regular compounding.Savings Goal Calculatormonthly saving = (goal − current) ÷ monthsCalculate the monthly saving needed to reach a goal.Salary Calculatorhourly = salary ÷ (52 × hours/week)Convert annual salary to monthly, weekly, daily, and hourly estimates.Hourly Rate Calculatorannual = hourly rate × hours/week × 52Convert hourly rate and weekly hours into weekly, monthly, and annual income.Rent Affordability Calculatoraffordable rent = monthly income × rent budget %Estimate a comfortable monthly rent from income and target rent percentage.Credit Card Payoff Calculatorbalance decreases monthly by payment minus monthly interestEstimate months to pay off a credit card balance with fixed monthly payments.Debt-to-Income CalculatorDTI = monthly debt ÷ gross monthly income × 100Calculate debt-to-income ratio from monthly debt payments and monthly income.Emergency Fund Calculatortarget fund = monthly expenses × months of coverageEstimate how much to save for an emergency fund.Inflation Calculatorfuture cost = amount × (1 + inflation rate)^yearsEstimate future buying power after inflation.APR to Monthly Rate Calculatormonthly rate = APR ÷ 12Convert annual percentage rate into an approximate monthly interest rate.Net Income Calculatornet income = gross × (1 − deductions %)Estimate net income after a flat tax or deduction percentage.Auto Loan Calculatorpayment = amount financed × monthly rate formulaEstimate monthly car loan payments from vehicle price, down payment, trade-in, rate, and term.Amortization Calculatorpayment = P × r(1+r)^n ÷ ((1+r)^n − 1)Estimate monthly payment, total interest, and payoff schedule summary for an amortized loan.Mortgage Payoff Calculatornew payoff months simulate balance + interest − payment − extraEstimate how extra monthly payments can shorten a mortgage payoff timeline.Investment Calculatorfuture value = compounded initial + compounded monthly contributionsEstimate future investment value with monthly contributions and annual return.Retirement Calculatorfuture retirement balance = current savings growth + contribution growthEstimate retirement savings at retirement from current savings, contributions, return, and years.Rent vs Buy Calculatorownership cost = mortgage payment + monthly taxes/insurance/HOACompare rough monthly rent cost against estimated monthly ownership cost.Debt Payoff Calculatormonthly payoff simulation with interestEstimate time to pay off a debt using fixed monthly payments.Budget Calculatorcategory amount = income × category percentageSplit monthly income into needs, wants, savings, and remaining money.Take Home Pay Calculatortake home = gross − tax − benefitsEstimate take-home pay after tax, benefits, and other deductions.APR CalculatorAPR ≈ finance charge ÷ amount ÷ days × 365 × 100Estimate APR from finance charge, loan amount, and loan term.Monthly Payment Calculatorpayment = P × r(1+r)^n ÷ ((1+r)^n − 1)Calculate monthly payment for a loan amount, annual rate, and term.Overtime Calculatorpay = regular hours × rate + overtime hours × rate × multiplierCalculate regular pay, overtime pay, and total weekly pay.Biweekly Paycheck Calculatorbiweekly pay = annual salary ÷ 26 or hourly rate × hours × 2Estimate biweekly pay from annual salary or hourly work.Weekly Paycheck Calculatorweekly pay = salary ÷ 52 or hourly rate × weekly hoursEstimate weekly gross pay from salary or hourly rate.Annual Income Calculatorannual income = amount × periods per yearConvert hourly, daily, weekly, or monthly income into annual income.Pay Raise Calculatornew salary = current salary × (1 + raise% ÷ 100)Calculate new salary, raise amount, and raise percentage.Cost of Living Calculatorrequired salary = current salary × new index ÷ current indexCompare salary needs between two cost-of-living levels.Cashback Calculatorcashback = spending × rate ÷ 100Calculate cashback rewards from spending and reward rate.Credit Card Interest Calculatormonthly interest = balance × APR ÷ 100 ÷ 12Estimate monthly credit card interest from balance and APR.Minimum Payment Calculatorminimum payment = max(balance × percent, fixed minimum)Estimate a credit card minimum payment using percent plus fees.Net Worth Calculatornet worth = assets − liabilitiesCalculate net worth from total assets and liabilities.Savings Rate Calculatorsavings rate = savings ÷ income × 100Calculate savings rate from income and savings.Rule of 72 Calculatordoubling years ≈ 72 ÷ annual return rateEstimate how long it takes money to double at a fixed return rate.Real Interest Rate Calculatorreal rate ≈ ((1 + nominal) ÷ (1 + inflation) − 1) × 100Estimate real return after inflation.Taxable Income Calculatortaxable income = gross income − deductionsEstimate taxable income after deductions.Property Tax Calculatorannual property tax = property value × tax rate ÷ 100Estimate yearly and monthly property tax.Closing Cost Calculatorclosing costs = home price × closing cost rateEstimate home purchase closing costs as a percent of price.Down Payment Calculatordown payment = price × percent ÷ 100Calculate down payment amount and remaining loan amount.Price Per Square Foot Calculatorprice per sq ft = total price ÷ square feetCalculate property or project price per square foot.