The Library of Instruments

GEOMETRY TOOLS

Geometry Construction Studio

A hands-on geometry drawing board for constructions, measurements, and clean diagram exports.

FRACTIONS

Fraction Calculator

Fraction arithmetic, simplification, comparison, and conversion in one focused tool.

GENERAL

Scientific Calculator

Full scientific keypad for trig, logs, roots, powers, memory, Ans, and angle modes.

ARITHMETIC

Percentage Calculator

Percent of a number, percent share, and increase or decrease in one place.

GEOMETRY

Triangle Calculator

SSS, SAS, or base-height triangle solving with side, angle, area, and perimeter results.

GEOMETRY

Volume Calculator

Cuboid, cube, cylinder, cone, and sphere volume calculator.

STATISTICS

Standard Deviation Calculator

Standard deviation from a pasted number list with sample or population choice.

GENERAL

Random Number Generator

Random integers or decimals with range, count, and duplicate settings.

GENERAL

Number Sequence Calculator

Sequence pattern finder for next terms and likely rule recognition.

ARITHMETIC

Percent Error Calculator

Percent error from measured and accepted values.

ALGEBRA

Exponent Calculator

Base-and-exponent power calculator.

NUMBER SYSTEMS

Binary Calculator

Binary-to-decimal, decimal-to-binary, and binary expression calculator.

NUMBER SYSTEMS

Hex Calculator

Hex-to-decimal, decimal-to-hex, and hexadecimal expression tool.

SCIENCE

Half-Life Calculator

Remaining amount from initial quantity, half-life, and elapsed time.

ALGEBRA

Quadratic Formula Calculator

Quadratic roots from a, b, and c in ax² + bx + c = 0.

ALGEBRA

Slope Calculator

Slope from two points with line-form details.

ALGEBRA

Log Calculator

Custom-base logarithm calculator.

GEOMETRY

Area Calculator

Area calculator for rectangles, triangles, circles, and trapezoids.

STATISTICS

Sample Size Calculator

Sample size estimate from confidence level, margin, and expected proportion.

STATISTICS

Probability Calculator

Simple, independent, and complement probability calculator.

STATISTICS

Statistics Calculator

Full descriptive statistics summary from a number list.

STATISTICS

Mean, Median, Mode, Range Calculator

Mean, median, mode, and range from a pasted number list.

STATISTICS

Permutation and Combination Calculator

nPr and nCr calculator for counting problems.

STATISTICS

Z-score Calculator

Z-score from value, mean, and standard deviation.

STATISTICS

Confidence Interval Calculator

Confidence interval for a sample mean.

ARITHMETIC

Ratio Calculator

Ratio simplifier, equivalent ratio solver, and proportion splitter.

GEOMETRY

Distance Calculator

Coordinate distance and speed-times-time distance in one tool.

GEOMETRY

Circle Calculator

Radius, diameter, circumference, and area solver for one circle.

GEOMETRY

Surface Area Calculator

Surface area for cube, cuboid, cylinder, cone, and sphere.

GEOMETRY

Pythagorean Theorem Calculator

Solve the unknown side of a right triangle.

GEOMETRY

Right Triangle Calculator

Right triangle solver for two sides or a side-and-angle setup.

ALGEBRA

Root Calculator

Square root, cube root, and n-th root calculator.

NUMBER THEORY

Least Common Multiple Calculator

Least common multiple from multiple integers.

NUMBER THEORY

Greatest Common Factor Calculator

Greatest common factor from multiple integers.

NUMBER THEORY

Factor Calculator

Factor list calculator for one integer.

ARITHMETIC

Rounding Calculator

Rounding by decimals, place values, or significant figures.

ALGEBRA

Matrix Calculator

Matrix addition, subtraction, multiplication, determinant, and inverse.

GENERAL

Scientific Notation Calculator

Scientific notation conversion in both directions.

GENERAL

Big Number Calculator

Exact arithmetic for very large whole-number expressions.

NUMBER THEORY

Prime Factorization Calculator

Prime factorization for one integer.

NUMBER THEORY

Common Factor Calculator

Common factors shared by multiple integers.

GENERAL

Basic Calculator

Basic four-function calculator with expression input.

ARITHMETIC

Long Division Calculator

Long division calculator for dividends and divisors.

ARITHMETIC

Average Calculator

Average calculator from a number list.

STATISTICS

P-value Calculator

P-value from z, t, or chi-square test statistics.

HEALTH AND FITNESS

BMI Calculator

Metric or imperial BMI estimate with weight-status screening ranges.

HEALTH AND FITNESS

Calorie Calculator

Daily calorie estimate for maintenance, loss, or gain using body details and activity level.

HEALTH AND FITNESS

Body Fat Calculator

Body-fat estimate from neck, waist, height, and hip when required.

HEALTH AND FITNESS

BMR Calculator

Metric or imperial BMR estimate from age, sex, height, and weight.

HEALTH AND FITNESS

Macro Calculator

Macro split estimate from body details, activity, and goal.

HEALTH AND FITNESS

Ideal Weight Calculator

Reference weight estimate with separate child and adult handling.

HEALTH AND FITNESS

Pregnancy Calculator

Pregnancy timeline estimate from last period or due date.

HEALTH AND FITNESS

Pregnancy Weight Gain Calculator

Pregnancy weight-gain range from prepregnancy measurements and current week.

HEALTH AND FITNESS

Pregnancy Conception Calculator

Likely conception-date estimate from common pregnancy dates.

HEALTH AND FITNESS

Due Date Calculator

Expected due date from LMP, conception date, or IVF transfer.

HEALTH AND FITNESS

Pace Calculator

Pace, time, and distance solver for walking or running.

HEALTH AND FITNESS

Army Body Fat Calculator

Army tape-test body-fat estimate from age, sex, weight, and abdomen measurement.

HEALTH AND FITNESS

Carbohydrate Calculator

Daily carbohydrate target from body details, activity, and goal.

HEALTH AND FITNESS

Lean Body Mass Calculator

Lean body mass estimate from weight and body-fat percentage.

HEALTH AND FITNESS

Healthy Weight Calculator

Height-based healthy weight range calculator.

HEALTH AND FITNESS

Calories Burned Calculator

Calories-burned estimate from weight, exercise intensity, and time.

HEALTH AND FITNESS

One Rep Max Calculator

One-rep max estimate from a recent lifting set.

HEALTH AND FITNESS

Target Heart Rate Calculator

Target heart-rate zone estimate for moderate and vigorous exercise.

HEALTH AND FITNESS

Protein Calculator

Daily protein target in grams from weight, activity, and goal.

HEALTH AND FITNESS

Fat Intake Calculator

Daily fat-gram estimate from calorie target.

HEALTH AND FITNESS

TDEE Calculator

TDEE estimate from body size and activity level.

HEALTH AND FITNESS

Ovulation Calculator

Cycle-based ovulation and fertile-window estimate.

HEALTH AND FITNESS

Conception Calculator

Likely conception-date estimate from due date or cycle timing.

HEALTH AND FITNESS

Period Calculator

Next period and cycle-date estimate from recent period history.

HEALTH AND FITNESS

GFR Calculator

eGFR estimate from creatinine, age, and sex.

HEALTH AND FITNESS

Body Type Calculator

Body-shape profile from common upper- and lower-body measurements.

HEALTH AND FITNESS

Body Surface Area Calculator

Body surface area estimate from height and weight.

HEALTH AND FITNESS

BAC Calculator

Approximate BAC estimate from drinks, time, sex, and body weight.

HEALTH AND FITNESS

Anorexic BMI Calculator

BMI estimate with severe-underweight screening warning.

HEALTH AND FITNESS

Weight Watcher Points Calculator

Legacy points-style food estimate from calories, fat, and fiber.

HEALTH AND FITNESS

Overweight Calculator

BMI-based overweight screening check from height and weight.

FINANCE

Mortgage Calculator

Mortgage payment estimate with escrow-style housing costs and amortization context.

FINANCE

Loan Calculator

Fixed-rate loan payment and amortization estimate from amount, rate, and term.

FINANCE

Auto Loan Calculator

Car-loan payment estimate with trade-in, tax, fees, and payoff summary.

FINANCE

Interest Calculator

Simple-interest versus compound-interest growth in one finance tool.

FINANCE

Payment Calculator

Periodic payment solver for borrowing or for reaching a future savings target.

FINANCE

Retirement Calculator

Retirement projection with current savings, future contributions, and inflation-aware output.

FINANCE

Amortization Calculator

Amortization-focused payment schedule for a fixed-rate installment loan.

FINANCE

Investment Calculator

Investment growth estimate with compounding and optional recurring additions.

FINANCE

Currency Calculator

Currency conversion estimate with optional custom exchange-rate control.

FINANCE

Inflation Calculator

Inflation-based future value and buying-power comparison in one place.

FINANCE

Finance Calculator

Time-value-of-money solver for core finance equations and cash-flow timing questions.

FINANCE

Mortgage Payoff Calculator

Extra-payment mortgage payoff estimate with interest-savings focus.

FINANCE

Income Tax Calculator

Federal income tax estimate using filing status and current bracket rules.

FINANCE

Compound Interest Calculator

Compound-interest growth estimate with recurring deposits or additions.

FINANCE

Salary Calculator

Pay conversion tool for hourly wages, salaries, and regular work schedules.

FINANCE

401K Calculator

401(k) growth estimate with employee savings and employer-match support.

FINANCE

Interest Rate Calculator

Loan-rate solver from borrowed amount, periodic payment, and term length.

FINANCE

Sales Tax Calculator

Sales-tax add-on and reverse-tax calculator for shopping and invoicing.

FINANCE

House Affordability Calculator

Home affordability estimate from income, debt load, and mortgage assumptions.

FINANCE

Savings Calculator

Savings growth estimate from deposits, rate, and time horizon.

FINANCE

Rent Calculator

Rent-cost summary with optional income-ratio context for housing planning.

FINANCE

Marriage Tax Calculator

Marriage-bonus or marriage-penalty estimate from federal filing-status comparison.

FINANCE

Estate Tax Calculator

Federal estate-tax estimate above the exclusion amount.

FINANCE

Pension Calculator

Defined-benefit pension estimate from service, salary, and payout formula.

FINANCE

Social Security Calculator

Social Security retirement estimate with claim-age adjustment context.

FINANCE

Annuity Calculator

Future annuity value estimate from recurring payments and growth rate.

FINANCE

Annuity Payout Calculator

Annuity-withdrawal estimate from starting balance, rate, and payout term.

FINANCE

Credit Card Calculator

Credit-card payoff estimate from balance, APR, and monthly payment size.

FINANCE

Credit Cards Payoff Calculator

Combined credit-card payoff estimate for total revolving debt.

FINANCE

Debt Payoff Calculator

Debt payoff estimate with payoff time, total outflow, and interest cost.

FINANCE

Debt Consolidation Calculator

Debt-consolidation comparison between current debt structure and a replacement loan.

FINANCE

Repayment Calculator

Repayment-time estimate from balance, rate, and monthly payment.

FINANCE

Student Loan Calculator

Student-loan payment estimate with schedule and total interest context.

FINANCE

College Cost Calculator

Projected future college cost based on today's tuition and expected annual increases.

FINANCE

Simple Interest Calculator

Simple-interest and maturity-value estimate without compounding.

FINANCE

CD Calculator

CD maturity estimate with interest earned over the selected term.

FINANCE

Bond Calculator

Bond return estimate with coupon income, current yield, and approximate yield to maturity.

FINANCE

Mutual Fund Calculator

Mutual-fund growth estimate with contributions and fee impact.

FINANCE

Roth IRA Calculator

Roth IRA projection with future-value planning for tax-free qualified withdrawals.

FINANCE

IRA Calculator

Traditional IRA growth estimate with annual contribution planning.

FINANCE

RMD Calculator

RMD estimate from prior year-end balance and IRS lifetime factors.

FINANCE

VAT Calculator

VAT add-on and reverse-VAT calculator for invoice and pricing work.

FINANCE

Cash Back or Low Interest Calculator

Cash-rebate versus low-rate financing comparison for major purchases.

FINANCE

Auto Lease Calculator

Vehicle lease-payment estimate from cap cost, residual, and money factor.

FINANCE

Depreciation Calculator

Depreciation estimate by method, elapsed time, and residual value assumptions.

FINANCE

Average Return Calculator

Average-return and CAGR calculator for investment-performance comparison.

FINANCE

Margin Calculator

Profit-margin and markup calculator for pricing and sales decisions.

FINANCE

Discount Calculator

Discount-value and final-price calculator for pricing and promotions.

FINANCE

Business Loan Calculator

Business-loan payment estimate with full amortization context.

FINANCE

Debt-to-Income Ratio Calculator

Monthly DTI estimate from recurring obligations and gross income.

FINANCE

Real Estate Calculator

Real-estate investment snapshot with NOI and cap-rate style outputs.

FINANCE

Take-Home-Paycheck Calculator

Paycheck estimate after federal tax and FICA withholding.

FINANCE

Personal Loan Calculator

Personal-loan payment estimate with full installment schedule.

FINANCE

Boat Loan Calculator

Boat-financing payment estimate with repayment and interest summary.

FINANCE

Lease Calculator

General lease-payment estimate for non-auto lease structures and asset financing.

FINANCE

Refinance Calculator

Mortgage-refinance comparison with break-even and payment-change focus.

FINANCE

Budget Calculator

Simple monthly budget summary with income, expenses, and savings targets.

FINANCE

Rental Property Calculator

Rental-property return estimate with cash flow and cap-rate metrics.

FINANCE

IRR Calculator

IRR estimate from an investment outlay and projected future cash-flow stream.

FINANCE

ROI Calculator

ROI percentage and profit estimate from cost and ending value.

FINANCE

APR Calculator

APR estimate that reflects loan cash flow and up-front financing costs.

FINANCE

FHA Loan Calculator

FHA loan-payment estimate with upfront and annual mortgage-insurance costs.

FINANCE

VA Mortgage Calculator

VA mortgage estimate with funding-fee treatment and payment summary.

FINANCE

Home Equity Loan Calculator

Home-equity loan payment estimate with fixed-rate amortization detail.

FINANCE

HELOC Calculator

HELOC estimate with interest-only draw phase and later repayment phase.

FINANCE

Down Payment Calculator

Down-payment estimate with financed amount and LTV clarity.

FINANCE

Rent vs. Buy Calculator

Rent-versus-buy comparison using housing cost, time horizon, and ownership assumptions.

FINANCE

Payback Period Calculator

Payback-period estimate from upfront cost and recurring annual cash flow.

FINANCE

Present Value Calculator

Present-value estimate that turns future dollars into today's equivalent value.

FINANCE

Future Value Calculator

Future-value estimate with compounding and optional recurring additions.

FINANCE

Commission Calculator

Commission amount and total compensation estimate from sales value.

FINANCE

Mortgage Calculator UK

UK mortgage-payment estimate from property value, deposit, and borrowing terms.

FINANCE

Canadian Mortgage Calculator

Canadian mortgage-payment estimate with monthly or biweekly repayment options.

FINANCE

Mortgage Amortization Calculator

Mortgage-payment and amortization summary with housing-loan context.

FINANCE

Percent Off Calculator

Percent-off sale-price calculator with savings amount and optional tax.

EVERYDAY

Age Calculator

Exact age finder with years, months, days, and total elapsed time.

EVERYDAY

Date Calculator

Date arithmetic and date-difference calculator in one workflow.

EVERYDAY

Time Calculator

Clock-time arithmetic with hour, minute, second, and day-offset output.

EVERYDAY

Hours Calculator

Work-hours calculator with break deduction for a single shift.

EDUCATION

GPA Calculator

Course-grade GPA estimate with optional credit-hour weighting.

EDUCATION

Grade Calculator

Required-final-grade calculator for target course results.

CONVERSION

Height Calculator

Height conversion tool across metric and imperial formats.

CONSTRUCTION

Concrete Calculator

Concrete volume estimate in cubic feet, cubic yards, and cubic meters.

NETWORKING

IP Subnet Calculator

IPv4 subnet breakdown with mask, network, broadcast, and usable range.

SIZING

Bra Size Calculator

Band-and-cup size starting estimate from two body measurements.

UTILITIES

Password Generator

Random password generator with length and character-type controls.

FUN

Dice Roller

Virtual dice roller with custom sides, quantity, and modifier.

CONVERSION

Conversion Calculator

General length conversion across metric and imperial units.

TRAVEL

Fuel Cost Calculator

Trip fuel-cost estimate from distance, efficiency, and fuel price.

ELECTRICAL

Voltage Drop Calculator

Voltage-drop estimate with remaining load voltage output.

HVAC

BTU Calculator

Room BTU estimate for quick cooling-capacity planning.

CONSTRUCTION

Square Footage Calculator

Area calculator for rooms, flooring, walls, and simple rectangular spaces.

WORK

Time Card Calculator

Time-card total with payable hours and optional hourly-pay estimate.

TIME

Time Zone Calculator

Time-zone converter for local date, time, and offset changes.

FUN

Love Calculator

Fun name-based compatibility score with a lighthearted result.

ECONOMICS

GDP Calculator

GDP-per-capita estimate from total GDP and population size.

TRAVEL

Gas Mileage Calculator

Fuel-economy calculator with MPG, km/L, and L/100 km results.

AUTOMOTIVE

Horsepower Calculator

Horsepower estimate from torque and RPM with kilowatt equivalent.

AUTOMOTIVE

Engine Horsepower Calculator

Power conversion between horsepower and kilowatts.

CONSTRUCTION

Stair Calculator

Stair layout helper with riser count and run estimate.

ELECTRICAL

Resistor Calculator

Equivalent-resistance calculator for resistor networks.

ELECTRICAL

Ohms Law Calculator

Ohm's-law solver for the missing V, I, or R quantity.

ELECTRICAL

Electricity Calculator

Power, kWh, and electricity-cost estimate from appliance use.

SIZING

Shoe Size Conversion

Shoe-size conversion across major regional sizing standards.

EVERYDAY

Tip Calculator

Tip and bill-splitting calculator for dining and service payments.

TRAVEL

Mileage Calculator

Trip mileage summary with optional fuel-cost-per-distance output.

SCIENCE

Density Calculator

Density solver from mass and volume inputs.

SCIENCE

Mass Calculator

Mass solver from density and volume values.

SCIENCE

Weight Calculator

Weight-force calculator from mass and gravity.

PHYSICS

Speed Calculator

Average-speed calculator from trip distance and travel time.

CHEMISTRY

Molarity Calculator

Molarity solver for solution concentration in mol/L.

CHEMISTRY

Molecular Weight Calculator

Formula-to-molar-mass calculator for chemistry notation.

CONVERSION

Roman Numeral Converter

Two-way Roman numeral converter for classical numbering.

SPORTS

Golf Handicap Calculator

Golf handicap estimate with separate modern and legacy modes.

HEALTH

Sleep Calculator

Sleep-duration and sleep-cycle helper from bedtime and wake time.

AUTOMOTIVE

Tire Size Calculator

Tire-dimension calculator from width, aspect ratio, and wheel diameter.

CONSTRUCTION

Roofing Calculator

Roof area and roofing-square estimate with waste allowance.

CONSTRUCTION

Tile Calculator

Tile-count estimate with waste percentage for floors and walls.

GARDEN

Mulch Calculator

Mulch-volume estimate in cubic feet and cubic yards.

CONSTRUCTION

Gravel Calculator

Gravel estimate in cubic volume and approximate tons.

WEATHER

Wind Chill Calculator

Wind-chill estimate from temperature and wind speed.

WEATHER

Heat Index Calculator

Heat-index estimate from temperature and relative humidity.

WEATHER

Dew Point Calculator

Dew-point estimate from temperature and humidity.

NETWORKING

Bandwidth Calculator

Transfer-time estimator from file size and network speed.

UTILITIES

Base64 Encode / Decode

Base64 encoder and decoder for common text-conversion tasks.

UTILITIES

URL Encode / Decode

URL encoding and decoding for query strings and web text.

TIME

Time Duration Calculator

Date-time duration calculator for full elapsed-time measurement.

TIME

Day Counter

Day-count calculator for inclusive and exclusive calendar spans.

TIME

Day of the Week Calculator

Weekday finder for a chosen calendar date.

OTHER

Auto Year Calculator

VIN model-year lookup for modern 17-character vehicle identification numbers.