Calculators, converters, generators and tools for every day
From maths and money to text, colour, dates and code, Hopi has a tool for the everyday question in front of you. The maths tools handle percentages, fractions, ratios, averages and standard deviation. The money and UK tools work out VAT, take-home pay, income tax, National Insurance, mortgages, loans, compound interest, stamp duty, holiday entitlement and salaries on the current tax year. The converters switch between length, weight, volume, temperature, speed and dozens of other units, from kilograms to stones and centimetres to feet. The text tools count words and characters, change case and tidy up writing, while the colour tools convert between hex, RGB and HSL and build palettes. There are date and time tools for ages, countdowns, days between dates and working days, random generators for passwords, dice, names, coin flips and lottery numbers, health and fitness tools for BMI, calories, TDEE and running pace, developer tools for JSON, Base64, hashing, UUIDs and regular expressions, crypto tools for Bitcoin and Ethereum, and file tools to resize images and merge PDFs.
Every tool runs entirely in your browser, so nothing you type, paste or upload is ever sent to us, seen by us or stored by us. You can choose to share a result through a link that carries the values you typed, but that is always your choice, and files you open stay private in your browser and can never be shared this way. The tools are built mobile-first, load fast, need no sign-up, and most can be installed to your desktop or home screen so they open in a single tap. Where it matters, they use UK rates and measurements, from the current tax year to stones and pounds.
Frequently asked questions
Are the tools on Hopi free?
Yes. Every calculator, converter and generator on Hopi is completely free to use, with no account, no sign-up and nothing to download. The site is funded by a small amount of advertising.
Is my data private?
Yes. Every tool runs entirely in your web browser, and nothing you type, paste or upload is ever sent to us or stored by us. Many calculators let you share a result through a link that carries the values you typed, but that is always your choice, and files you open can never be shared this way and never leave your device. The only tool that contacts a server is the currency converter, which fetches current exchange rates from Hopi's own server.
Do the tools work on my phone?
Yes. Every tool is built mobile-first and works in any modern browser on a phone, tablet or computer, with no app to install.
Can I add a tool to my home screen or desktop?
Yes. Most tools can be installed as their own app using the Add to desktop button, so they open in a single tap and keep working offline once loaded.
Who is Hopi for?
Anyone who needs a quick, reliable answer. The tools use UK rates and measurements where it matters (VAT, take-home pay, stones and pounds), and every calculator shows its formula so you can trust the result.