How our estimates work.
Each calculator separates the formula from the interface, documents its inputs and outputs, and keeps external assumptions visible.
Research before formula
Material coverage, package rules, installation constraints, and conversion factors are checked against manufacturer or authoritative sources where feasible. Competitor tools help us understand common expectations; they are not treated as the source of truth.
Units and rounding
US units are the default. Metric values are converted at the input and output boundaries, while formulas use a canonical internal unit. Display values are rounded for readability; material packages round up and raw need remains available where it changes the decision.
Charts that answer a question
Each result shows a breakdown only when it helps a decision: what each coat uses, how much of an order is allowance versus whole-package rounding, or how a budget splits between material, installation, and supplies. Diagrams such as tile layouts, wallpaper drops, and carpet runs are drawn to scale from your inputs, and every chart has a text legend with the same numbers.
Worked examples are tested
The worked example on each calculator page uses the calculator’s default inputs. An automated test checks that the live result matches the example, so the explanation and the tool cannot drift apart.
Waste and allowances
An allowance is a project control, not a guarantee. Pattern, room geometry, cuts, seams, defects, repairs, and installer experience all change the correct amount. Replace the example with your product or installation guidance.
Sources we rely on
Unit conversions use exact definitions (1 ft = 0.3048 m). Coverage, allowance, and sizing guidance come from manufacturer documentation and established guidance such as product technical data sheets, paint and primer labels, grout coverage charts, and retailer installation guides. Each guide links the sources it cites. Where sources disagree, we show a range and keep the value editable.
Review and corrections
Every calculator and guide shows the date it was last reviewed. When a reader reports a problem through the contact form, we recheck the formula and sources, rerun the tests, correct confirmed errors, and update the review date.
Independence
The site is supported by advertising. Advertisers have no influence on formulas, defaults, or content, and ads never sit between a calculator’s inputs and its result.
Privacy
Basic calculations run in the browser. Room measurements are not sent to a server or stored by this site.