About BuildLumi
BuildLumi is a free website of construction calculators and material estimators for US homeowners, DIYers and contractors, with formulas and sources shown on every calculator and guide.
What BuildLumi is
You enter the measurements of a slab, a garden bed, a wall or a roof. BuildLumi gives you the volume, area or count, plus the steps it took to get there. There is no signup, and the calculators run in your browser. The calculator directory lists all 20 calculators available today, and the 27 guides explain the math behind the most common questions.
Who it is for
- Homeowners and DIYers planning a patio, a fence, a deck, a flower bed or a drywall repair.
- Contractors and builders who want a quick second opinion on a takeoff.
- Anyone who needs to convert between square feet, cubic yards, tons and metric units without trusting a black box.
How the calculators are built
- Verified sources. Formulas, yields and conversion factors come from standards bodies, manufacturer data sheets and university extension publications. Where only an industry convention exists, it is labeled as one.
- Formulas shown. Every result lists its steps, from your inputs to the final number.
- Editable assumptions. Waste, compaction, density and bag size are defaults. Change them to match your project and your supplier.
- Tested. Each calculator has automated tests that compare its output with independently computed examples.
The details, including exact unit conversions and rounding rules, are on the methodology page.
Editorial standards
- How figures are sourced. Every number comes from a named source, such as a standards body, a manufacturer data sheet or a university extension publication, or from plain arithmetic shown on the page. Each source lists the date it was accessed. Where only an industry convention exists, it is labeled as one and stays editable.
- Confidence labels. Figures are rated higher, medium or low confidence by the kind of source behind them, and sources that are not primary are marked as secondary. The methodology page explains the labels and lists the sources for each calculator.
- Review dates. Guides show the date they were last updated, and calculator pages show when they were last reviewed. A date changes only when the numbers have been checked against their sources again.
- Worked examples. Examples are checked arithmetically before they are published, and the same numbers are used wherever a topic repeats.
- Corrections. If a figure looks wrong, write through the contact page with the calculator, your inputs and the result you expected. The number is checked against its original source before it is changed.
What BuildLumi is not
- It is not engineering. The calculators estimate quantities. They do not size footings, slabs, joists, rafters or fasteners for loads.
- It is not a contractor or an inspector, and it does not replace your local building department or a licensed professional.
- It does not sell building products. Product names that appear on the site identify the data sheets we used; BuildLumi has no affiliation with those companies.
Read the calculation disclaimer before you order materials.
How it is funded
BuildLumi is free to use. In the future the site may show advertising to cover its costs. If that happens, this page and the privacy policy will be updated before any ads appear, and the calculators will stay free.
Contact and corrections
Found a wrong number, a unit that is unclear, or a calculator you would like to see? Write to [email protected] or use the contact page. Corrections are checked against the original source before the site is changed.