About FreeToolbox24 & how we calculate

FreeToolbox24 is a small set of free calculators for home improvement and DIY projects. Each one answers a single practical question – how much paint, how many tiles, how many bags of concrete – before you spend money.

Our method

• Formulas shown on every page. Each calculator states the exact formula, the assumptions (such as the area of a standard door) and a worked example you can check by hand.
• Metric and imperial. Every calculator accepts metres and feet. Conversions use exact factors (1 ft = 0.3048 m, 1 US gallon = 3.785 L, 1 yd³ = 0.7646 m³).
• Waste margins. Real projects lose material to cuts, breakage and uneven surfaces. Where it matters we add a stated margin (usually 5–15%) and tell you what it is.
• Manufacturer data first. Coverage rates, bag yields and product sizes are typical values from common products. Your product label always wins – most calculators let you enter your own figure.

Limits

Results are estimates for planning and shopping. They are not structural, electrical or engineering advice. For load-bearing structures, roofs, retaining walls over 1 m (3 ft) and anything covered by local building codes, check with a qualified professional and your local authority.

Corrections

Found a mistake or a product size we should add? Every page is reviewed regularly and the review date is shown at the bottom of each calculator.