All tools
Free browser-based tools and calculators — no install, no signup.
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Math & Numbers
Calculator
A simple, fast online calculator for everyday arithmetic.
Scientific Calculator
A simple scientific calculator with trigonometric, logarithmic and power functions.
Interest Calculator
Calculate compound interest growth with optional monthly contributions.
Unit Converter
Convert between length, mass, volume, and temperature units.
Bill Splitter
Split a bill with tip between any number of people.
Percentage Calculator
Calculate percentages, find what percent one number is of another, or work out percent change — all in one tool.
Loan Calculator
Calculate your monthly loan payment, plus the total amount and interest you'll pay over the life of the loan.
Discount Calculator
Work out the final price after one or two stacked percentage discounts, and see exactly how much you saved.
VAT Calculator
Add VAT to a net price or remove VAT from a gross price, and see the net amount, gross amount, and tax amount at a glance.
Tip Calculator
Quickly work out how much to tip, split the total with friends, and see what everyone owes.
Audio & Music
Metronome
A free online metronome to practice music at any tempo.
Tuner
A free online chromatic tuner that listens to your instrument through the microphone.
BPM Tap Tempo
Tap along to a song's beat to instantly find its tempo in beats per minute.
Audio Bitrate Calculator
Calculate the file size of an audio track from its bitrate and duration, or work out the bitrate needed to hit a target file size.
Fitness & Sports
One-Rep-Max Calculator
Estimate your one-rep max (1RM) from any weight and rep count, with a training percentage table.
Running Pace Calculator
Calculate your running pace and speed from distance and time, with predicted race finish times.
Heart Rate Zone Calculator
Find your personal training heart rate zones from your age and resting heart rate using the Karvonen formula.
Swim Pace Calculator
Calculate your swimming pace per 100 meters or yards from distance and time, with predicted times for common distances.
VO2 Max Calculator
Estimate your VO2 max from your age and resting heart rate, no exercise test required.
Design & Photo
Exposure Calculator
Find equivalent camera exposures across aperture, shutter speed, and ISO.
Aspect Ratio Calculator
Scale an image or video proportionally and find its simplified ratio.
CSS Gradient Generator
Design a linear or radial CSS gradient and copy the generated code.
Contrast Checker
Check whether a foreground and background color meet WCAG contrast guidelines.
Color Palette Generator
Turn any base color into complementary, analogous, and triadic color palettes.
Color Format Converter
Convert any color between HEX, RGB, HSL, and CMYK instantly, with one-click copy for each format.
Typography Scale Generator
Generate a harmonious set of font sizes from a base size and a scale ratio, ready to copy as CSS custom properties.
Developer Tools
Regex Tester
Test regular expressions against sample text with live match highlighting.
Cron Expression Parser
Parse a 5-field cron expression into a plain-language schedule and see its next run times.
Text Encoding Converter
Convert text to UTF-8 hex, binary, code points, Base64, URL encoding and HTML entities at once.
Password Generator
Generate strong, random passwords instantly, right in your browser.
JSON Formatter & Validator
Format, validate, and minify JSON instantly in your browser.
UUID Generator
Generate random, RFC 4122 version 4 UUIDs instantly in your browser.
JWT Decoder
Decode and inspect JSON Web Tokens (JWTs) instantly in your browser.
Diff Checker
Compare two blocks of text and instantly see every line that was added or removed.
Slug Generator
Turn any text into a clean, URL-friendly slug in real time.
Number Base Converter
Convert numbers between binary, octal, decimal, and hexadecimal instantly.
Unix Timestamp Converter
Convert Unix timestamps to dates and dates to Unix timestamps, live.
Hash Generator
Generate SHA-1, SHA-256, and SHA-512 hash digests from any text, right in your browser.
Box Shadow Generator
Design a CSS box-shadow visually with live sliders and a color picker, then copy the generated declaration.
Cron Expression Builder
Build a valid 5-field cron expression from a friendly form — no need to memorize the syntax.
Lorem Ipsum Generator
Generate placeholder Lorem Ipsum text by paragraphs, sentences, or words for mockups and layouts.
Markdown Previewer
Write Markdown on the left and see the rendered HTML update live on the right.
IP Subnet Calculator
Enter an IPv4 address in CIDR notation and get its network, mask, broadcast, and host range.
HTTP Status Code Lookup
Look up any HTTP status code and see its standard meaning in plain English.
SQL Formatter
Pretty-print minified or messy SQL into readable, indented statements.
Image to Base64 Converter
Convert an image into a Base64 data URI you can paste straight into HTML, CSS, or JSON — entirely in your browser.
Semver Comparator
Compare two semantic version strings and see which one takes precedence, following the official semver rules.
Kitchen & Cooking
Recipe Converter
Scale ingredient quantities to any number of servings and convert cooking volume units.
Oven Temperature Converter
Convert oven temperatures between Celsius, Fahrenheit, and UK Gas Mark in an instant.
Coffee Ratio Calculator
Dial in the perfect coffee-to-water ratio for pour-over, French press, AeroPress, or espresso.
Pizza Dough Calculator
Calculate exactly how much flour, water, salt, and yeast you need for perfect pizza dough, in any batch size.
Air Fryer Conversion Calculator
Convert a conventional oven temperature and time into the equivalent air fryer setting.
Health & Family
Due Date Calculator
Estimate your baby's due date and current week of pregnancy from your last period or conception date.
BMI Calculator
Calculate your Body Mass Index (BMI) from your height and weight, in metric or imperial units.
Calorie Calculator (TDEE)
Estimate your daily calorie needs — BMR and TDEE — from your age, height, weight and activity level.
Body Fat Calculator
Estimate your body fat percentage from neck, waist, and height measurements using the U.S. Navy method.
Sleep Cycle Calculator
Find the best time to go to bed or wake up, based on 90-minute sleep cycles.
Water Intake Calculator
Estimate how much water to drink each day based on your body weight, activity level and climate.
Macro Calculator
Split a daily calorie target into protein, carb and fat grams based on your diet goal.
Time & Productivity
World Clock
See the current time in multiple timezones at a glance.
Pomodoro Timer
A free online Pomodoro timer for focused work and regular breaks.
Business Days Calculator
Count the number of working days (Monday through Friday) between two dates.
Age Calculator
Find out exactly how old you are — in years, months, and days — and how long until your next birthday.
Timezone Meeting Planner
Find a meeting time that works across timezones — see what your proposed hour looks like for everyone on the list.
Work Hours Calculator
Calculate how many hours you worked from your clock-in and clock-out times, minus any unpaid break.
Why Thunder Tools
Thunder Tools bundles dozens of small, focused calculators and converters into one fast, ad-light site — everything runs right in your browser, so your numbers and files never get uploaded anywhere. New tools are added regularly, and every one of them is free to use without an account.
Frequently asked questions
- Is Thunder Tools really free?
- Yes — every tool is completely free to use, with no account, subscription or hidden paywall.
- Do I need to create an account?
- No. All tools work immediately in your browser, without any sign-up.
- Is my data uploaded anywhere?
- No — every tool runs entirely client-side, in your browser. Whatever you type, calculate or convert stays on your device and is never sent to a server.
- Which languages does Thunder Tools support?
- The site is available in 12 languages, including English, German, French, Spanish, Italian and Japanese — switch anytime with the language selector in the header.
- Do the tools work on mobile?
- Yes — every tool is responsive and works just as well on a phone or tablet as on a desktop.
- How often are new tools added?
- Regularly — the collection keeps growing with new calculators and converters, so it's worth checking back.