Free Online Calculators
Material estimates for DIY projects, math tools with exact answers, and health calculators, each with the formula written out and a worked example.
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- Formulas shownEvery page writes out the math and walks through a worked example.
- Rounded the right wayMaterial counts round up to whole bags and boxes; math answers stay exact.
- Sources citedCoverage figures and health guidance link to where they come from.
All Calculators
Construction & DIY
Concrete, paint, flooring, drywall, decks, fences and landscaping.
- Concrete CalculatorBags and cubic yards for slabs, footings and post holes.
- Paint CalculatorGallons and quarts of paint and primer for walls and ceilings.
- Gravel CalculatorCubic yards, tons and bags of gravel or crushed stone.
- Mulch CalculatorBags or cubic yards of mulch, topsoil and compost for any bed.
- Flooring CalculatorBoxes of laminate, vinyl plank or hardwood, with layout waste.
- Tile CalculatorTiles and boxes for floors, walls and backsplashes, with waste.
- Drywall CalculatorSheets of 4×8, 4×10 or 4×12 drywall for walls and ceilings.
- Deck CalculatorDeck boards, linear feet and joists for a rectangular deck.
- Fence CalculatorPosts, rails, pickets and post concrete for a wood fence.
Math
Graphing, fractions, algebra and derivatives.
- Algebra CalculatorSolve linear, quadratic and cubic equations, or simplify expressions.
- Derivative CalculatorFirst, second and third derivatives, evaluated at any point.
- Fraction CalculatorAdd, subtract, multiply and divide fractions and mixed numbers.
- Graphing CalculatorPlot up to three functions and find their intercepts.
Health
Sleep timing and everyday health tools.
- BMI CalculatorBody mass index, CDC weight category and healthy weight range.
- Body Fat CalculatorBody fat percentage from tape measurements (U.S. Navy method).
- Ideal Weight CalculatorHealthy weight range for your height, plus four classic formulas.
- BMR CalculatorCalories burned at rest, using the Mifflin–St Jeor equation.
- Calorie CalculatorDaily calories to maintain weight, at four activity levels.
- Water Intake CalculatorDaily water needs for adults, from National Academies intakes.
- Sleep CalculatorBedtimes and wake-up times that line up with full sleep cycles.
- Due Date CalculatorEstimated due date from last period, conception or IVF transfer.
Finance
Loans, savings and everyday money math.
- Auto Loan CalculatorCar payment with trade-in, sales tax and fees included.
- Loan CalculatorMonthly payment, total interest and amortization for any fixed-rate loan.
- Mortgage CalculatorFull monthly mortgage payment, including taxes, insurance and PMI.
- Credit Card Payoff CalculatorMonths to pay off a card balance, or the payment needed to clear it.
- Debt Payoff CalculatorSnowball vs avalanche plan for paying off several debts.
- Federal Income Tax Calculator 20262026 US federal income tax by filing status, with bracket breakdown.
- Sales Tax CalculatorAdd sales tax to a price, or remove it from a total.