Free calculators for the trades. No ads, no accounts, works offline.
roughlogic.com is 2,267 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 |
Under every example the page names the published sources that calculator is checked against, or says plainly that none is on file. Every page has a Details, formula, and sources drop-down if you want to check the math; where a citation names a free official source, such as nfpa.org/freeaccess or a federal regulation like 29 CFR 1926.502, it links straight to it. On most calculators a Show the steps panel under the answer goes further: every input as it was used and every intermediate value worked out on the way to the answer, so you can show an inspector how you got the number.
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.
Every fix is recorded in the open. The site's corrections log lists each changelog fix that names a calculator, newest first, with a link to the full write-up.
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.
npm run lint accounts for every numbered spec and checks its status against the calculator catalog. Historical status formats are normalized; renamed calculators need explicit built as mappings, and later removals must name every retired ID.
MIT. See LICENSE.
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