How to use the Basic Calculator
Learn the keypad, keyboard shortcuts, percent discounts, one-step math behavior, copy result action, and tab-only calculation history.
Read guideFree calculator guides and utility how-tos
Find the guide behind each live Access Free Tools page. Browse calculators, converters, browser AI tools, and home project estimators with examples, formulas, input notes, limits, links back to the matching tool, and a few owner notes about building the library.
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Type a tool name, formula, or project word to jump straight to the matching guide.
Showing first 36 of 303 guides. Search or show all to browse every guide.
Percentage Calculator Guide: Reverse Percentages
Learn three reverse-percentage setups, percent change, discounts, and how to recover an original value before an increase or decrease.
Read guideRatio Calculator Guide
Learn how to simplify ratios, scale equivalent ratios, split totals, handle decimals, check units, and avoid swapped-part mistakes.
Read guidePercent Error Calculator Guide
Learn how to compare measured and accepted values, read signed percent error, match units, handle zero-value limits, and avoid lab-report mistakes.
Read guideHow to use the Half-Life Calculator
Learn how to calculate remaining amount, elapsed time, and half-life with matching units, examples, privacy notes, and safety limits.
Read guideHow to use the Exponent Calculator
Learn how to calculate powers, negative and zero exponents, decimal and fraction exponents, scientific notation, 0^0 limits, and common exponent mistakes.
Read guideHow to use the Log Calculator
Learn custom-base logs, ln, log10, change-of-base steps, valid input rules, negative log answers, exponent checks, and common mistakes.
Read guideHow to use the Root Calculator
Learn square roots, cube roots, nth roots, decimal radicands, exponent form, power checks, negative-root limits, and common mistakes.
Read guideAbsolute Value Calculator Guide
Learn absolute value, distance from zero, signed difference, absolute difference, number-line examples, and common mistakes.
Read guideHow to use the Quadratic Formula Calculator
Learn coefficient signs, standard form, discriminants, real roots, repeated roots, complex roots, graph details, and answer checks.
Read guideHow to use the Binary Calculator
Learn how to add, subtract, multiply, divide, and convert binary numbers with base-2 place values, decimal checks, and remainders.
Read guideHow to use the Hex Calculator
Learn how to add, subtract, multiply, divide, and convert hex numbers with decimal, binary, color-code, remainder, and signed-value checks.
Read guideHow to use the Kawaii Calculator
Learn when to use the cute pastel calculator, how its buttons and shortcuts work, and how to keep recent calculations private in the browser.
Read guideHow to use the Scientific Calculator
Learn DEG/RAD mode, typed expressions, trig functions, logs, roots, powers, constants, history, and when this tool is useful.
Read guideHow to use a Fraction Calculator with steps
Calculate, simplify, compare, and convert fractions, mixed numbers, whole numbers, and terminating decimals with exact steps.
Read guideLCM Calculator Guide
Learn how to find the least common multiple of two or more whole numbers, read the steps, and use LCM for fractions and schedules.
Read guideGCF Calculator Guide
Learn how to find the greatest common factor, compare GCF with LCM, simplify fractions, and read exact integer steps.
Read guideHow to use the Factor Calculator
Learn how to list factors, factor pairs, prime factors, and prime factorization for positive whole numbers.
Read guideHow to use the Prime Factorization Calculator
Learn how to read prime factors, exponent form, factor trees, special cases like 1, and GCF or LCM checks.
Read guideHow to use the Long Division Calculator
Learn how quotient, remainder, decimal form, and the multiplication check work in whole-number long division.
Read guideHow to use the Rounding Calculator
Learn how to round by decimal places, significant figures, and place value using nearest, up, down, and truncate methods.
Read guideMatrix Calculator Guide
Check 2x2 and 3x3 matrix addition, multiplication, transpose, and determinant steps with plain examples.
Read guideHow to use the Scientific Notation Calculator
Learn how to convert standard numbers to scientific notation and convert coefficient-times-power-of-10 form back to standard form.
Read guideWhy BigInt Keeps Huge Integer Math Exact
Learn why normal numbers round past the safe-integer limit and how BigInt keeps exact digits, quotients, and remainders.
Read guideHow to use the Standard Deviation Calculator
Learn how to calculate sample or population standard deviation, variance, mean, count, formula steps, examples, and practical limits from one data set.
Read guideHow to use the Number Sequence Calculator
Learn how to generate arithmetic, geometric, and Fibonacci-style sequences, read formulas, check term limits, and avoid common pattern mistakes.
Read guideHow to use the Sample Size Calculator
Learn how to estimate completed survey responses with confidence level, margin of error, population proportion, finite population correction, and response-rate planning.
Read guideHow to use the Probability Calculator
Learn how to read P(A or B), P(A and B), complements, independent-event overlap, impossible inputs, and probability limits.
Read guideHow to use the Statistics Calculator
Learn how to read count, sum, mean, median, mode, range, quartiles, IQR, variance, and sample or population standard deviation.
Read guideHow to use the Average Calculator
Learn how to find the arithmetic mean, check the sum and count, and compare average with median, mode, and range.
Read guideMean, Median, Mode, Range Calculator Guide
Learn how to enter a data set, check mean, median, mode, and range formulas, and spot outliers, ties, and no-mode cases.
Read guidePermutation and Combination Guide
Learn when to use nPr or nCr, how order changes counting, how no-replacement formulas work, and how to read exact examples.
Read guideHow to use the Z-score Calculator
Learn how to standardize a value, read above-or-below-average direction, and estimate a normal percentile.
Read guideHow to use the P-value Calculator
Learn how to choose the tail, enter a z-score, read standard-normal p-values, and avoid common interpretation mistakes.
Read guideHow to use the Confidence Interval Calculator
Learn how to calculate z confidence intervals for a mean or proportion with margin of error and clear formula steps.
Read guideCan Three Sides Form a Triangle? SSS Guide
Check the triangle inequality, find a possible third-side range, and work through valid and invalid three-side examples.
Read guideOwner notes
Field notes from building a free tools site
These posts explain what I am testing behind the scenes: useful software, search lessons, writing checks, and safer ways to grow without turning the site into filler.
8 Open-Source Projects Behind Access Free ToolsBrendan Chambers explains how Astro, React, TypeScript, Playwright, Vitest, Tesseract.js, Transformers.js, and Ollama each earn a specific job behind the site.How I Check a GitHub Project Before Installing ItThe repository, license, install-script, dependency, write-location, and sandbox checks Brendan uses before adding an open-source project.Browser AI vs Local AI: What Stays on Your Device?Brendan Chambers explains which inputs stay on a device, which model files download, and when browser, local, and cloud AI still make network requests.
Reader-first guides
Start with a guide that explains the result
Use these guides to check what each input means, how the tool calculates the result, which mistakes change the answer, and when you should treat the answer as an estimate.
Basic calculator guideLearn quick arithmetic, keyboard input, percent keys, and history checks.Percentage examplesSee discounts, markups, percent change, reverse percentages, and common mistakes.Absolute value examplesUse distance from zero, signed difference, and absolute difference without mixing up direction and size.Ad revenue estimatesUnderstand pageviews, RPM, CTR, CPC, and why earnings estimates are not promises.Battery capacity conversionConvert amp-hours to watt-hours with voltage and compare battery capacity more clearly.Watts to amps safety notesUse watts, volts, phase, and power factor for current estimates, then check the electrical limits.Image to text OCRUse browser OCR, improve image quality, and understand privacy and accuracy limits.Wallpaper waste percentEstimate rolls and learn why waste percent matters for cuts and pattern matching.
Browse by job
Pick the topic before the tool name
Start with the kind of problem first. Then move to the exact tool or guide that matches the question.
Math and everyday calculatorsStart with calculator guides for percentages, fractions, exponents, roots, statistics, and quick arithmetic.Finance calculator guidesUse these when the result depends on rates, terms, taxes, income, payments, or assumptions.Home project calculator guidesCompare material estimates for concrete, wallpaper, sand, gravel, paint, roofing, and yard projects.Electrical calculator guidesMove from watts, amps, kW, and kVA to Ohm's law, energy cost, voltage drop, and wire-planning limits.Health and fitness guidesRead formula limits, privacy notes, and when an estimate should not replace professional advice.Browser AI tool guidesLearn how browser-side OCR, language checks, keyword extraction, and reading tools handle privacy and limits.All free toolsJump back to the full searchable tool library when you already know the calculator you need.
Useful starting points
Calculator guide shortcuts
Start with guides for common calculator questions: interest, sales tax, savings, CDs, roofing, large numbers, dates, gas mileage, fractions, markup, and watts to amps.
Personal loan calculator guideCompare payment, cash received after an origination fee, APR-style cost, total interest, and lender warning signs before accepting an offer.Interest rate guideEstimate the annual rate hidden inside a fixed payment and check the loan inputs that change it.Sales tax guideCalculate tax amount, final price, and reverse-tax checks from a before-tax or after-tax number.Ad revenue calculatorUse pageviews, RPM, CPC, and CTR without treating a website earnings estimate like a payout.Why BigInt keeps huge integers exactSee the safe-integer boundary, exact quotient and remainder rules, and the check behind large integer division.Savings calculator guideEstimate a savings target with starting balance, deposits, interest rate, compounding, and time.APY calculator guideConvert a stated deposit rate and compounding frequency into estimated APY, term interest, and ending balance.CD calculator guideCompare deposit, APY, term length, compounding, and interest earned without ignoring early-withdrawal risk.Markup guideCompare markup, margin, selling price, cost, and profit without mixing up the formulas.Fraction guideCalculate, simplify, compare, and convert fractions, mixed numbers, whole numbers, and decimals with exact steps.Date calculator guideCount days between dates, add or subtract days, and avoid calendar-range mistakes.Gas mileage guideCompare miles, gallons, MPG, trip cost, and fuel-price assumptions before you trust the number.Engine horsepower guideSolve horsepower, torque, RPM, engine HP, and wheel HP while keeping loss assumptions visible.Roofing calculator guidePlan roof material estimates with area, pitch, waste, bundle counts, and supplier checks.Watts to amps guideUse watts, volts, phase, and power factor for current estimates, then check electrical limits.Watts to amps calculatorOpen the calculator when you know watts and voltage and need a current estimate.
When details matter
Guides for assumptions, limits, and real examples
These guides are good starting points when the answer depends on an exchange rate, loan rule, measurement method, material estimate, token price, or platform limit.
VA mortgage funding fee guideCheck first-use, later-use, exemption, financed-fee, tax, and insurance assumptions before reading the payment.Currency conversion guideUse a manual exchange rate, fee percent, inverse-rate check, and provider-rate warning without treating it as live FX data.FHA loan payment guideCompare down payment, upfront MIP, monthly MIP, tax, insurance, and FHA approval limits in plain language.Monthly budget guideBreak income, spending, debt, and savings into a monthly snapshot with leftover-money and savings-rate checks.Markdown table guideClean pasted rows, headers, separators, and alignment before using a table in docs, READMEs, or issue comments.Character counter guideCompare characters, no-space characters, words, lines, and UTF-8 bytes for titles, forms, snippets, and messages.AI token cost guideEstimate prompt, completion, and model-cost scenarios without confusing tokens, words, and API billing units.Distance formula between two pointsSubstitute coordinate changes, check distance squared, keep exact square roots, and separate straight-line math from map routes.Battery runtime from mAh, mA, or wattsChoose the right runtime formula, calculate a duty-cycle average, and account for usable capacity and conversion loss.How much soil do I need?Measure one or several beds, choose the fill depth and bag size, then compare bags, litres, and bulk cubic yards.How to measure sidingMeasure walls and gables, choose an opening method, add waste, and turn exact siding squares into whole boxes.Brick wall calculation formulaCalculate wall area, subtract openings, compare brick-and-joint coverage with supplier tables, and add waste.
Useful starting points
Tools and guides for common jobs
Start here for writing checks, calculators, converters, loan examples, and project estimates that often need a little more explanation than the answer alone.
Color contrast checkerCheck WCAG-style contrast ratios for text, backgrounds, buttons, disabled states, and focus states.Reading level checkerEstimate grade level, reading ease, sentence length, and long-word signals before publishing help copy.Love calculator guideUse the playful name match carefully and understand why the result is only for fun.Mileage calculator guideCalculate mileage reimbursement from miles, rate per mile, parking, tolls, and extras without confusing it with MPG.Concrete calculator guideEstimate slab, footing, column, and bag needs with cubic-yard checks and ordering limits.Deck stain calculator guidePlan stain quantity from deck area, coats, coverage rate, railings, and weather-related waste.Lawn mowing calculator guideEstimate mowing time or price from lawn size, speed, obstacles, and trimming assumptions.Mean median mode range guideCheck average, median, most common value, range, and outlier effects with a small data set.Repayment calculator guideCompare payment, term, balance, and interest assumptions before trusting a payoff estimate.Right triangle guideSolve missing sides, angles, area, and perimeter while checking hypotenuse and unit mistakes.RMD calculator guideEstimate required minimum distributions with age, balance, life-expectancy divisor, and IRS-limit cautions.Converters image galleryBrowse approved converter artwork tied back to live converter tools and guide pages.