About Hopi

Hopi is a growing collection of free online calculators, converters and generators, made in the UK. Percentages, VAT, dates, colours, passwords, units: the small questions that everyday life keeps asking.

What we believe a tool should be

• Instant. Answers appear as you type. No submit buttons where none are needed, no waiting.
• Private. Every tool runs entirely in your browser. Text you paste, dates you enter and passwords you generate never leave your device.
• Honest. Each page shows its formula and worked examples, so you can check the maths yourself.
• Free. No accounts, no sign-ups, no paywalls. The site is supported by a small amount of advertising.

UK first

Plenty of calculator sites exist; most of them speak American. Hopi's money tools use UK rates and UK rules (VAT at 20%, the current tax year, stones and pounds) and everything is written in British English.

Spotted a mistake, or is there a tool you wish existed? Tell us. The collection grows all the time and suggestions genuinely steer what gets built next.