Answers you can verify.
Calculators, conversions and practical answers. 72 of them, and not one number without a source.
The formula, printed
Not a result out of a black box. The working is on the page.
Sources, named and dated
Beside the value they justify, with the day they were read.
Your figures, kept
Change any input. The link you copy reopens on your numbers.
Home & constructionAll 10
- Concrete CalculatorSlab volume, bags to buy, waste allowance.
- Square Footage CalculatorEnter the length and width to get the area in square feet, square yards and square metres.
- Tile CalculatorEnter the area and your tile size to see the tiles needed, the boxes to buy and the spares left over.
- Flooring CalculatorEnter the room area and the coverage printed on the box to see how many boxes to buy.
- Roofing CalculatorEnter the footprint and the pitch to get the true sloped area, in square feet and in squares.
- Fence CalculatorEnter the run and your spacing to see the posts, sections, rails and pickets.
- Mulch CalculatorEnter the bed area and the depth you want to see the volume and the bags to buy.
- Brick CalculatorEnter the wall, the brick and the joint. Openings come off the area, and the order is shown apart from the net count.
- Gravel CalculatorEnter the area and the depth you want when it is finished and rolled. The answer is what to order, not what fits in the hole.
- Paint CalculatorEnter the room and the coverage printed on the tin. Openings come off, coats multiply, and whole tins are what you buy.
MathAll 23
- Percentage CalculatorEnter a percentage and a number to see the amount, plus the totals with it added and removed.
- Percentage Change CalculatorEnter the starting value and the new value to see how much it changed, in percent.
- Percentage Difference CalculatorEnter two values to compare them without either one being treated as the starting point.
- Fraction to Decimal CalculatorEnter a numerator and a denominator to see the decimal, the percentage and the simplest form.
- Ratio CalculatorEnter two quantities to see the ratio reduced, split as percentages and expressed as 1 to n.
- Rule of Three CalculatorIf A corresponds to B, what corresponds to C? Both proportions are solved at once.
- Reverse Percentage CalculatorYou have the number after the change. This finds the one before it.
- Circle CalculatorEnter a radius. Everything else about the circle follows from it.
- Triangle Area CalculatorTwo ways to the same answer, depending on which measurements you actually have.
- Probability CalculatorEnter the probability of each event to see how they combine.
- Bayes Theorem CalculatorEnter how common the condition is and how the test performs to see what a positive result really implies.
- Combination CalculatorEnter how many items there are and how many you take to see the combinations and permutations.
- Z-Score CalculatorEnter a value with the mean and standard deviation of its distribution.
- Confidence Interval CalculatorEnter your sample mean, standard deviation and size to see the interval around it.
- Sample Size CalculatorEnter the margin of error you want and the size of the group you are studying.
- Fraction CalculatorEnter two fractions to see the result of all four operations, each reduced to its simplest form.
- Exponent CalculatorEnter a base and an exponent to see the result.
- GCD & LCM CalculatorEnter two positive integers to see their GCD, LCM and how the two relate.
- Pythagorean Theorem CalculatorEnter the two legs of a right triangle to find the hypotenuse, or enter the hypotenuse and one leg to find the other.
- Quadratic Formula CalculatorEnter the coefficients a, b and c of ax² + bx + c = 0.
- Average CalculatorPaste or type your numbers, separated by spaces, commas or line breaks.
- Standard Deviation CalculatorPaste or type your numbers to see how spread out they are.
- Random Number GeneratorSet a range and how many numbers you need, then press Generate.
MoneyAll 17
- Loan Payment CalculatorMonthly payment, full schedule, and what a longer term really costs.
- Mortgage CalculatorPayment with taxes and insurance, and when mortgage insurance really ends.
- Compound Interest CalculatorYear-by-year growth, and what the balance is worth in today’s money.
- Auto Loan CalculatorPayment with tax, fees and trade-in — and when the car is finally worth more than you owe.
- Amortization CalculatorEvery payment dated, and what a lump sum is worth depending on when you pay it.
- Credit Card Payoff CalculatorHow long the minimum really takes, and the three-year payment your statement is required to show.
- Refinance CalculatorWhether replacing your loan costs less — counting what you owe, not just the payment.
- Debt Payoff CalculatorAvalanche against snowball on your own debts, and what the choice really costs.
- Savings CalculatorWhat regular monthly savings grow to over time, and when interest overtakes your deposits.
- Home Affordability CalculatorHow much house your income allows, worked backwards from the 28/36 rule.
- Discount CalculatorEnter the original price and the discount to see the sale price and the saving.
- Margin CalculatorEnter what an item costs you and what you sell it for.
- Markup CalculatorEnter your cost and the markup you want to apply to get the price to charge.
- Tip CalculatorEnter the bill and the percentage. Tax is kept separate, because tipping on tax is a choice.
- ROI CalculatorEnter what you put in, what you got back, and how long it took.
- Simple Interest CalculatorEnter the principal, the annual interest rate and the time to see what simple interest costs or earns.
- Sales Tax & VAT CalculatorEnter a price and a rate. The tax-exclusive and tax-inclusive figures are both shown.
HealthAll 13
- Pace CalculatorPace, speed and an exact split table for a target — metric and imperial together.
- BMI CalculatorEnter height and weight. The formula is shown, and so are its limits.
- Calorie & TDEE CalculatorTDEE is a resting figure multiplied by an activity guess. The first comes from a laboratory, the second is a convention — this page keeps them apart instead of blending them into one number.
- BMR CalculatorThe equation predicts to within 10% of a measured rate. This page shows that band, because a single figure hides it.
- Ideal Weight CalculatorThe four formulas agree closely. This page shows how narrow that agreement is next to the healthy range it hides inside.
- Body Fat CalculatorThe tape gives a percent; the method gives a band around it. This page shows both, because the band is wide enough to matter.
- Lean Body Mass CalculatorThe three formulas look like they agree. This page shows how far apart they are, and the body-fat range that gap leaves open.
- Body Surface Area CalculatorThe four formulas agree closely at an average build. This page shows the spread, and where it grows — the sizes at which the choice of formula starts to matter.
- One Rep Max CalculatorEnter a weight and the reps you managed with it. The three formulas rarely agree exactly, and the fewer the reps, the more you can trust the answer.
- Target Heart Rate CalculatorThe three formulas agree at middle age and pull apart at the edges. This page shows the spread, and treats the target zone as a band rather than a line.
- Waist-to-Height Ratio CalculatorOne rule: keep your waist under half your height. This page gives the ratio and how far your waist is from that line.
- Macro CalculatorEnter your daily calories. This page gives the macro ranges the science supports, in grams — and explains why a single “perfect” split is a preference, not a rule.
- Calories Burned CalculatorPick an activity’s MET, your weight and your minutes. This page gives both standard forms of the answer and is honest that the MET is a group average, not your number.
ConversionsAll 6
- Length ConverterEnter a length in any unit to see it in all the others at once.
- Area ConverterEnter an area in any unit to see it in all the others at once.
- Volume ConverterEnter a volume in any unit to see it in all the others at once.
- Weight ConverterEnter a weight in any unit to see it in all the others at once.
- Speed ConverterEnter a speed in any unit to see it in all the others at once.
- Temperature ConverterEnter a temperature in any scale to see it in the other two, and what a change of that size means.