Numbers you can act on, not just numbers you can read.
Every calculator here works the same way: enter your numbers, and get a result that's already passed a known-answer test before publication — not a formula that just looks plausible.
Categories
Construction & Materials
Volume, material and layout calculators for concrete, decking, fencing, paving, roofing and stairs.
Finance & Work
Pay, pricing and time calculators for wages, raises, overtime and markup.
Home & Utilities
Everyday household calculators for pools, appliances and energy costs.
Date & Time
Calendar-aware calculators for ages, dates and durations.
Popular calculators
Sand Calculator
Estimate how much sand you need by volume, weight and bag count from your project dimensions.
Topsoil Calculator
Work out how many cubic yards, bags and pounds of topsoil your garden bed or lawn project needs.
Stone Calculator
Calculate how much gravel or crushed stone you need in cubic yards, tons and bags.
Markup Calculator
Find your markup percentage, selling price, profit and margin from cost and price.
Deck Board Calculator
Calculate how many deck boards you need based on deck size, board width, gap and waste.
Pool Water Volume Calculator
Calculate your pool volume in gallons or litres from its shape and dimensions.
Pay Raise Calculator
Calculate your new salary, raise amount and pay-period equivalents from a raise percentage.
Fence Calculator
Estimate fence panels, posts, rails and concrete from your fence length and layout.
Paver Calculator
Find how many pavers you need for a patio or walkway, including waste allowance.
Roof Pitch Calculator
Convert rise and run into roof pitch, slope percentage, angle and rafter length.
How every calculator is built
Formula reviewed against a reference source
Every calculation model and its assumptions are checked before any code is written — not adapted from a guess.
Tested against known answers
At least three test cases per calculator, including an edge case, plus independent unit-conversion checks.
Shown, not hidden
Every page shows the formula and a fully worked example — so you can check the math yourself, not just trust a black box.
Guides
Deeper reading on the ideas behind the calculators — unit conversions, formula explanations, and common mistakes.
Tons vs Cubic Yards: How Material Weight and Volume Relate
Why sand, stone and topsoil are sold by weight and measured by volume, and how to convert between them.
Markup vs Margin: Why the Same Profit Gives Different Percentages
Markup and margin measure the same dollar profit against different denominators — here's why that matters when pricing.
kWh Explained: What a Kilowatt-Hour Actually Measures
What a kilowatt-hour is, how it differs from a kilowatt, and how to estimate what an appliance costs to run.
Frequently asked questions
Are these calculators really free?
Yes, every calculator on this site is free to use with no account or sign-up required.
How do you verify a calculator's formula before publishing it?
Every calculator passes a minimum of three known-answer test cases, including at least one edge case, plus independent unit-conversion checks and input validation testing, before it goes live. See our methodology page for the full standard.
Do the calculators store or send my inputs anywhere?
Calculations run entirely in your browser. Your inputs are not required to be transmitted to a server to produce a result.
What should I do if a calculator gives a result that looks wrong?
Please report it — see the contact page. Formula corrections are treated as a priority, not a routine content update.