How these calculators are built
Every calculator here follows the same construction rules. This page explains them so you can judge the results rather than take them on trust.
One calculation engine, not sixteen
Area, volume, waste, package rounding and cost are implemented once as shared, tested functions. A tile calculation and a flooring calculation that describe the same rectangle produce the same area, to the last decimal, because they call the same code. That consistency is enforced by automated tests, not by care alone.
Units are converted, never approximated
Internally every measurement is stored in metric base units using the exact international definitions: one inch is 0.0254 metres, one pound is 0.45359237 kilograms, one US gallon is 231 cubic inches. Feet and inches are the display, not the storage. Switching between US and metric therefore keeps your project intact rather than converting an already-rounded number a second time.
Raw, planned and purchased are three different numbers
A result separates the area or volume you measured, the quantity after a waste allowance, the whole packages you need to buy, the coverage those packages actually give you, and the leftover. Conflating them is the most common way a material estimate goes wrong, so the interface keeps them visibly distinct.
Rounding has three different jobs
Mathematical precision is kept in full internally. Display rounding happens only at the moment a number is drawn, and adapts to magnitude so a result reads three gallons rather than 3.000000. Purchase rounding always goes up, because you cannot buy 8.6 boxes. Package counts include a tolerance so floating-point noise can never sell you an extra box you do not need.
Waste is an allowance, not a fact
Recommended waste percentages are planning practice: they reflect cuts, breakage, pattern matching and keeping a few spare pieces for repairs. They are not standards, and they are not right for every layout. Every waste value on this site is adjustable, is labelled as an assumption, and is shown separately from the measured quantity.
Product-dependent numbers are inputs, not constants
Box coverage, bag yield, bundle coverage, paint spread rate and material density vary by manufacturer and product. Where a value genuinely varies, this site asks for it or offers clearly-labelled presets you can change. It does not invent a universal figure and present it as fact.
What these calculators are not
These are material planning and purchasing tools. They are not structural engineering, not code compliance, and not a substitute for the installation instructions supplied with your product. Anything involving structural load, spans, electrical sizing or gas is deliberately out of scope.