Free online tools that just work

BMI Calculator (metric & imperial, with category)

Calculate your Body Mass Index in metric or imperial units, with category interpretation.

Length Converter (mm, cm, m, km, in, ft, yd, mi)

Convert between metric and imperial length units instantly. Includes mm, cm, m, km, inches, feet, yards, and miles.

Age Calculator (years, months, days, weeks, hours)

Calculate exact age in years, months, days, weeks, and hours from any birth date to any target date.

Percentage Calculator (% of, what %, % change)

Three percentage calculators in one: 'X% of Y', 'X is what % of Y', and percentage change between two values.

Tip Calculator (with bill split for groups)

Calculate tip and split a restaurant bill across any number of people. Quick presets for common tip percentages.

Temperature Converter (Celsius, Fahrenheit, Kelvin, Rankine)

Convert between Celsius, Fahrenheit, Kelvin, and Rankine. All four scales update at once.

Password Generator (cryptographically secure, with strength meter)

Generate strong random passwords using your browser's secure crypto API. Configurable length, character sets, and ambiguity filter.

Word Counter (with reading and speaking time)

Count words, characters, sentences, paragraphs, plus estimated reading and speaking time. Handles CJK languages correctly.

Countdown Timer (live, days/hours/minutes/seconds)

Live countdown to any future date and time. Updates every second; works for events, deadlines, launches, vacations.

Compound Interest Calculator (with monthly contributions)

See how an investment grows over time with compounding interest and optional monthly contributions. Customizable compounding frequency.

Weight Converter (kg, g, t, lb, oz, stone, mg)

Convert between metric and imperial mass units. Includes mg, grams, kilograms, tonnes, ounces, pounds, and stones.

Area Converter (m², ft², acre, hectare, tsubo)

Convert between metric, imperial, and Japanese area units. Includes m², km², hectare, ft², acre, mile², and tsubo.

Time Unit Converter (ms, s, min, h, days, weeks, months, years)

Convert between time units from milliseconds to years. Months use the average length, years use the Julian definition.

Data Size Converter (B, KB, MB, GB, TB — SI and IEC)

Convert digital storage sizes between bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. Switch between SI (1000) and IEC binary (1024).

Calorie Calculator (BMR & TDEE, Mifflin-St Jeor)

Estimate your daily calorie needs using the Mifflin-St Jeor BMR formula and an activity multiplier. Includes targets for weight loss and gain.

Ideal Weight Calculator (Devine, Robinson, Miller, Hamwi)

Estimate ideal body weight using four classic clinical formulas plus the WHO healthy BMI range. Choose by height and sex.

Due Date Calculator (LMP or conception, with trimester)

Estimate your pregnancy due date from the last menstrual period or conception date. Includes gestational weeks and trimester.

color

Color Converter (HEX, RGB, HSL — instant)

Convert colors between HEX, RGB, and HSL with a live preview swatch. Edit any field; the others update.

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Contrast Checker (WCAG AA / AAA grades)

Check the color contrast ratio between text and background. Shows live preview and pass/fail badges for WCAG AA and AAA at normal and large text sizes.

Case Converter (camel, snake, kebab, Title, etc.)

Convert text into 10 case styles: UPPER, lower, Title, Sentence, camelCase, PascalCase, snake_case, kebab-case, CONSTANT_CASE, and inverted.

Base64 Encoder / Decoder (UTF-8 and URL-safe)

Encode any UTF-8 text to Base64 or decode it back. Toggle URL-safe encoding for use in URLs and JWTs.

JSON Formatter & Minifier (validates and pretty-prints)

Pretty-print or minify JSON. Validates the input and shows a clear error with line and column on failure.

Lorem Ipsum Generator (paragraphs, sentences, words)

Generate placeholder Latin text by paragraphs, sentences, or word count. Optional 'Lorem ipsum' opening line.

Loan Calculator (monthly payment, interest, total cost)

Calculate the monthly payment for any fixed-rate loan, plus total amount paid and total interest over the life of the loan.

Sales Tax / VAT Calculator (add tax or extract from total)

Add sales tax to a pre-tax amount or extract the tax from a tax-inclusive total. Works for any tax rate (sales tax, VAT, GST).

Discount Calculator (with optional sales tax)

Calculate the final price after a percentage discount, plus optional sales tax. See how much you saved at a glance.

GPA Calculator (4.0 scale, weighted by credits)

Calculate your GPA on the 4.0 scale, weighted by course credit hours. Add as many courses as you need.

Volume Converter (mL, L, gal, fl oz, cup, tsp)

Convert between metric and US/UK volume units. Includes mL, liters, m³, teaspoons, tablespoons, fluid ounces, cups, pints, quarts, and gallons.

Speed Converter (km/h, mph, m/s, knot, Mach)

Convert between common speed units: km/h, mph, m/s, ft/s, knots, and Mach. Used for vehicles, weather, aviation, and physics.

Fuel Economy Converter (mpg US/UK, km/L, L/100km)

Convert vehicle fuel economy between mpg (US), mpg (UK), km per liter, and L per 100 km. Distinguishes US and UK gallons.

URL Encoder / Decoder (percent-encoding, UTF-8 safe)

Encode any text into URL percent-encoding or decode an encoded string back. UTF-8 safe — handles emoji and CJK characters correctly.

Water Intake Calculator (daily target by weight)

Estimate your recommended daily water intake based on body weight and activity level. Shown in liters, ounces, cups, and bottle equivalents.

Roman Numeral Converter (1 to 3999, both directions)

Convert Arabic numbers to Roman numerals (and back). Validates canonical form so VIIII won't be silently accepted as 9.

Mortgage Calculator (PITI: principal, interest, tax, insurance)

Calculate the full monthly mortgage payment including principal, interest, property tax, insurance, PMI (if applicable), and HOA fees.

UUID Generator (v4 random, v7 time-ordered)

Generate cryptographically random UUID v4 or time-ordered UUID v7. Bulk-generate up to 100 at a time with one-click copy.

Unix Timestamp Converter (sec, ms, ISO, local)

Convert between Unix timestamps (seconds or milliseconds) and human-readable dates. Shows ISO 8601, local time, and relative time.

Number Base Converter (binary, octal, decimal, hex)

Convert numbers between binary, octal, decimal, and hexadecimal. Validates input for the chosen base and shows all four representations.

Random Number Generator (cryptographically secure, unique mode)

Generate random integers in any range using your browser's secure random API. Optionally enforce uniqueness for lottery, raffle, or sample-without-replacement use cases.

Text Diff Tool (line-level comparison, color-coded)

Compare two blocks of text line by line. Added, removed, and unchanged lines are color-coded with line numbers.

Regex Tester (live matches, groups, replace)

Test JavaScript regular expressions interactively. See live highlighted matches, capture groups, and a replace preview.

Paint Calculator (gallons or liters from room size)

Calculate how much paint you need based on room dimensions, number of coats, and doors/windows. Output in liters or gallons.

Markup Calculator (cost to sell price + margin)

Calculate sell price, gross profit, and gross margin from cost and markup percentage. Distinguishes markup vs margin clearly.

Running Pace Calculator (time, pace, speed)

Calculate running pace from distance and time, or finish time from a target pace. Output per-km, per-mile, km/h, and mph.

Macro Calculator (P/F/C grams from TDEE and goal)

Calculate daily protein, fat, and carb targets from your TDEE and weight goal. Uses 30/30/40 split with a protein floor of 1.6 g/kg.

Character Frequency Analyzer (letters, all chars, or words)

Count how often each character or word appears in your text. Sortable, with percentages, and optional case sensitivity.

Date Calculator (add/subtract days, or difference between dates)

Add or subtract years/months/days from a date, or find the precise difference between two dates including business days.

Timezone Converter (compare time across multiple zones)

Convert one moment in time across multiple timezones at once. Add or remove zones; great for scheduling international meetings.

Unit Price Calculator (compare cost per gram, oz, count)

Compare items by unit price (price per gram, ounce, count, etc.). Add as many items as you want; the cheapest is highlighted.

Hash Generator (SHA-1, SHA-256, SHA-384, SHA-512)

Compute SHA-1, SHA-256, SHA-384, and SHA-512 hashes of any UTF-8 text. Browser-native Web Crypto API; nothing leaves your device.

Email Validator (syntax + common typo detection)

Validate email address syntax against RFC 5322 and detect common typos in popular providers (gmail, yahoo, hotmail, etc).

Aspect Ratio Calculator (preserve ratio when resizing)

Calculate width or height to preserve a target aspect ratio. Common ratios (16:9, 9:16, 1:1, 4:3, 21:9) one-click presets included.

Find and Replace Text (literal or regex, with options)

Replace text with literal find/replace or full regex. Toggle case sensitivity and multi-line mode. Match count shown live.

Credit Card Validator (Luhn check + brand detection)

Validate a credit card number's checksum (Luhn algorithm) and detect the issuing brand. Browser-only — your card number never leaves your device.