35 calculators, no sign-up

Free calculators that show their working.

Material estimates, seller fees, margins, dates and everyday math. Every result comes with the formula behind it, so you can check the answer instead of trusting it.

Popular calculators

See all 35

Ecommerce

Twitch Bits to USD Calculator

Convert Twitch Bits to dollars from both sides: what the streamer receives and what the viewer paid to buy them.

Ecommerce

Stripe Fee Calculator

Calculate the Stripe processing fee and net payout on any charge, or reverse the maths to find the price that leaves you with an exact amount.

Time & Date

Time Duration Calculator

Measure the exact time between two dates and times, including overnight and multi-day spans, in days, hours, minutes and seconds.

Construction

Deck Material Calculator

Work out how many deck boards, joists and screws a deck needs from its length and width, with the waste allowance stated rather than hidden.

Math

Percentage Difference Calculator

Compare two values against their average to get the percentage difference — the symmetric measure that gives the same answer whichever value you enter first.

Ecommerce

PayPal Fee Calculator

See what PayPal takes from a payment and what reaches your balance, or work backwards to the amount you need to invoice to net an exact figure.

Construction

Roof Pitch Calculator

Convert between roof pitch, angle in degrees, grade and slope factor. Enter rise and run, an angle, or an x/12 pitch and get the other three.

Construction

Square Footage Calculator

Calculate square footage for rectangles, circles, triangles and trapezoids, in any unit, with conversions to square metres, yards and acres.

Browse by category

Calculators are grouped by the kind of problem they solve, so related tools sit together.

Construction8Material quantities for decking, concrete, paint, tile and aggregate, with the waste allowance stated rather than hidden.Ecommerce5Seller fee and profit calculators for the major marketplaces, with every fee rate left editable so a schedule change never makes the answer wrong.Business3Margin, markup, break-even and the pricing arithmetic that decides whether a sale is actually worth making.Math7Percentages, fractions, averages and the everyday arithmetic that is quicker to check than to do by hand.Time & Date5Work out ages, spans between dates, and totals of hours and minutes without counting on your fingers.Geometry2Ratios, triangles, area and volume — worked out from whichever measurements you actually have.Finance3Loan payments, interest growth and discounts, with the formula and assumptions behind every figure stated in full.Everyday Life1The small calculations that come up in ordinary life — splitting a bill, working out a tip, checking a total.Health1Body measurement calculators that state their formula, their source and, just as importantly, their limits.

Made to be checked.

The formula, every time

Each result comes with the substituted values and the steps, so you can check it or learn from it.

Instant and offline-friendly

Calculations run in your browser. Nothing is sent to a server, so results appear as fast as you type.

Assumptions stated plainly

Material estimates show their waste factor, and finance tools say where they stop being reliable rather than implying certainty.

Fees you can correct

Marketplace fee rates are editable inputs with the review date shown, so a schedule change never leaves you with a wrong answer.

Shareable results

Copy the result or share a link that reopens the calculator with the same values already filled in.

No account, no wall

Nothing is gated, nothing is tracked, and there is no account to make. Open a calculator and use it.