Free calculators for the trades. No ads, no accounts, works offline.
roughlogic.com is 2,183 small, single-purpose calculators for electricians, plumbers, HVAC techs, carpenters, firefighters, surveyors, and dozens of other trades. Every answer comes from a published formula and names its source.
Go to roughlogic.com.
Type the job the way you'd say it: voltage drop 120v 150 ft 12 awg 20a.
The answer shows at the top and updates as you type. Tap Copy to grab a value.
That's it. Bookmark any calculator and your numbers come with it. After the first visit it works with no signal.
Related MCP server: QuantOracle
From Voltage Drop:
You enter | You get | ||
Phase | single | Voltage drop | 7.45 V |
Material | copper | Percent drop | 3.11 % |
AWG | 10 | ||
Length one-way (ft) | 150 | ||
Current (A) | 20 | ||
Source voltage (V) | 240 |
Every page has a Details, formula, and sources drop-down if you want to check the math.
Electrical · Plumbing & gas · HVAC · Carpentry & construction · Water damage & mold · Fire ground · Trucking · Auto, marine & aviation · Agriculture · Water & wastewater · Stage production · Kitchens · Backcountry & SAR · Rigging · Lab math · Real estate · Small-business tax · Teaching, and more.
Everything runs in your browser. No account, no email, no tracking. The only thing that ever leaves your device is a problem report, and only if you choose to send one.
Claude, Cursor, and other agents can run every calculator through a small local server. See mcp/README.md.
Please open an issue with your inputs and the source that disagrees. It's the most useful report you can send.
npm ci # install dev tooling
npm run dev # build and serve locally
npm test # run the unit testsHow it's built and how every answer is tested: docs/how-it-works.md. Contributing: CONTRIBUTING.md.
MIT. See LICENSE.
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