How We Calculate
This page explains how each CalcHandy calculator is built, checked and kept up to date, so you know what stands behind the numbers you see.
1. We start from a published method
Every calculator begins with a standard formula or a published source, not a guess. Volume tools use geometry. Pay tools follow the rules payroll departments use, such as time and a half after 40 hours. Electrical sizing uses the copper ampacity table from the National Electrical Code and the resistance values in NEC Chapter 9. The tips deduction follows IRS guidance. Fee tools use each platform's own published fee pages.
2. We write the formula as code and test it
Each formula is a small, separate function with automated tests. The tests use inputs where we already know the right answer from a hand calculation, for example that 10 ft by 10 ft at 3 inches deep is 25 cubic feet. A change to the site cannot go live if a test fails.
3. We show the method on the page
Below every calculator you will find the formula in words, at least one worked example with real numbers, a reference table, a list of common mistakes and answers to frequent questions. The goal is that you could repeat the calculation with a pencil and get the same result.
4. We date and source anything that changes
Fees, tax rules and standards change. Pages that depend on them show a "last updated" date and, for fee calculators, a "fees last checked" date with a link to the official source. When we cannot confirm a current rate, we say so on the page and let you edit the rate yourself.
5. We state the limits
Each estimate has assumptions. Gravel density varies by stone type, air conditioner sizing depends on your climate and insulation, and a puppy's growth depends on its breed. We list the main assumptions and the situations where the answer changes, so you know when to ask a professional.
6. We fix mistakes
If you report an error, we check it against the source, correct the calculator or text and update the page date. You can reach us through the contact page.
Sources we rely on
- Electrical: the National Electrical Code (NFPA 70) ampacity Table 310.16 and the conductor resistance values in Chapter 9, Table 8.
- Pay and work: US Department of Labor guidance on the Fair Labor Standards Act, including overtime and the regular rate.
- Tax: IRS guidance on the no tax on tips deduction, IRS guidance on the no tax on overtime deduction, and the income tax brackets and standard deductions in IRS Revenue Procedures 2024-40 (tax year 2025) and 2025-32 (tax year 2026).
- Fees: each platform's own published pricing pages, linked on the calculator and dated.
- Materials and sizing: unit definitions, published density and coverage figures and common sizing rules, always stated on the page.
Corrections
We publish material corrections so that you can see what changed and when.
- November 12, 2026, Wire Gauge calculator: resistance for 14 to 8 AWG copper and 12 to 8 AWG aluminum changed from solid-conductor to stranded-conductor values, which raises the calculated voltage drop slightly.
- November 11, 2026, No Tax on Tips calculator: corrected the income phase-out. The $25,000 maximum is reduced as income rises above the threshold, and the deduction is the smaller of your qualified tips and that reduced maximum. An earlier version reduced the deduction itself, which understated it for people whose tips were below the reduced maximum.
- November 11, 2026, FAQ sections: fixed a display error that showed single letters instead of questions on some pages.
What we do not do
We do not collect your calculator inputs on a server, we do not ask you to sign up, and we do not let advertisers influence results. For how advertising and cookies work on the site, see the Privacy Policy.