Step-by-step guides on construction math, finance calculations, health formulas, and more — written by the team behind the calculators.
Overtime isn't taxed at a higher rate — withholding makes it look that way. Here's the bracket math, a worked example, and what overtime costs you in tax.
Most latex paint covers 350–400 sq ft per gallon. Here's the wall-area formula, a coverage table by paint type, and the coat-count mistakes that leave you short.
Mulch depth of 2–3 inches covers 108–162 sq ft per cubic yard. Here's the coverage table, bags-vs-bulk math, and the volcano-mulching mistake that kills trees.
Your waist-to-hip ratio reveals more about metabolic risk than BMI alone. Here's the WHO risk table, how to measure correctly, and what to do if yours is high.
Stair rise and run are tightly regulated by the IRC. Here's the formula, max/min limits, a worked example for a 9-ft deck, and the mistakes that cause most failed inspections.
Federal unsubsidized loans accrue interest from day one. Here's how capitalization works, what the standard repayment plan actually costs, and the salary rule that determines how much you can safely borrow.
Compound interest earns returns on your returns, not just principal. Here's the formula, a worked example, and why starting at 25 beats starting at 35.
Roof pitch is rise over 12 inches of run. Here's the formula, how to measure it yourself, and how pitch affects material quantity and labor cost.
Grass seed coverage rates vary by up to 40× depending on species. Here's the seeding rate table, the simple formula, and the mistakes that cause most failures.
Running burns 80–150 calories per mile depending on weight and pace. Here's the formula, a reference table, and why treadmill estimates run high.
The formula for calculating what grade you need on your final exam — with worked examples for 25%, 30%, and 40% weighted finals and a quick-reference table.
Minimum payments on a $3,000 balance at 20% APR take 14 years and cost nearly as much in interest as the debt itself. Here's the math and how to shorten it.
Step-by-step guide to estimating drywall for any room — wall sq ft math, ceiling, thickness selection, and the right waste factor to avoid a second trip.
Regular topsoil compacts and kills drainage. Here's the 60/30/10 soil mix that works, depth requirements by plant type, and how to calculate how much you need.
Daily protein recommendations range from 0.36 to 1 g per pound. Here's what the research says, how to calculate your target, and where most people go wrong.
Step-by-step guide to calculating cubic yards of concrete for any slab — with formulas, waste factors, bag counts, and a free calculator.
A plain-English guide to calculating your net paycheck — covering federal tax, FICA, state tax, and pre-tax deductions like 401(k) and health insurance.
Most students assume a 3 earns credit everywhere. It doesn't. Here's how AP credit thresholds work — by school type, by subject, and whether you should use the credit at all.
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