Free online calculators

• Aquarium Volume CalculatorWork out gallons, litres and filled weight for rectangular, cylinder, bow-front, hex and corner tanks.
• Board Foot CalculatorTotal board feet and cost for a cutlist, plus a log scale for rough logs.
• Business Days CalculatorCount business days between two dates, or add/subtract business days from a deadline — with US federal holidays.
• Coffee Ratio CalculatorDial in the perfect coffee-to-water ratio for pour-over, French press, AeroPress, cold brew, espresso and more.
• Concrete CalculatorConcrete calculator for slabs, footings, round columns and stairs — cubic yards and premix bags.
• Countdown CalculatorCount down to any date and time, with totals in weeks, days, hours and business days — shareable by link.
• Dilution CalculatorSolve C1V1 = C2V2, work out dilution ratios, and plan serial dilution series.
• Fabric CalculatorFabric calculator for curtains, yardage for any project, and yard/metre unit conversion.
• Golf Handicap CalculatorWorld Handicap System index from your last 20 rounds, plus course handicap for today's round.
• Overtime Pay CalculatorOvertime pay calculator with taxes: enter your hours and rate to see regular pay, OT pay, gross and estimated take-home.
• Prorated Rent CalculatorWork out partial-month rent for a mid-month move-in or move-out, compared across three proration methods.
• Quilt Backing and Binding CalculatorQuilt backing, binding and border yardage from your quilt top size.
• Running Pace CalculatorSolve pace, time or distance, get splits and a race-time predictor for any distance.
• Sourdough CalculatorBaker's-percentage sourdough calculator with true hydration, recipe scaling and a levain build helper.
• Time Card CalculatorA weekly time card calculator with lunch break deductions, overtime and pay totals.
• Tire Size CalculatorTire size calculator comparison: diameter, circumference, speedometer error and ride height between two tire sizes.

What these calculators do

These are single-purpose calculators for jobs that a general-purpose calculator site handles badly: how many cubic yards of concrete a slab needs, how much backing a quilt takes, what a partial month of rent comes to, what your running pace means in splits. Each one asks only for the numbers that calculation actually needs, and gives the answer as you type.

Every page writes out the formula it uses and works through a real example with real numbers, so you can check the result by hand or reuse the method somewhere else. Where a figure is an approximation rather than an exact answer — bow-front aquarium volume, the Doyle log scale, Riegel's race-time prediction, a flat-percentage take-home estimate — the page says so and says roughly how far off it can be. That matters more than it sounds: most wrong answers online come from a tool quietly applying an assumption you did not know about.

Nothing here needs an account and nothing you enter is uploaded. Pay rates, rent figures, scores and measurements are calculated by JavaScript in your own browser and disappear when you close the tab.

What every page includes

Whichever one you open, the layout is the same: the tool itself at the top so you can get an answer in a few seconds, then the formula and a worked example, then the questions people most often ask about that particular calculation, then links to the closest related tools. No cookie banner, no interstitial, no "create a free account to see your result".

Not what you were after? See every tool on FigureItFast, including the other categories, or read how these tools are built and checked.