Frequently Asked Questions
The questions we hear most about material estimating and how this site works. Every calculator page also has its own FAQ specific to that tool, and each guide answers the long-tail questions for its topic in depth.
Frequently Asked Questions
Are the HomeBuild Atlas calculators really free?
Yes. Every calculator is free, requires no account, and has no usage limits. The site is supported by advertising and affiliate links, which never affect the numbers the tools return.
How accurate are the calculators?
The math is exact; the inputs are the uncertainty. Formulas follow standard construction-estimating practice with documented waste, compaction, and swell factors. Measure carefully, use the defaults unless you know better values, and confirm final quantities with your supplier.
How much concrete do I need for a 10x10 slab?
At 4 inches thick: 1.23 cubic yards, or 1.5 cubic yards ordered with 10% waste. That's about 62 bags of 80 lb concrete mix - at that quantity, ready-mix delivery is usually the better choice.
How many bags of concrete equal one cubic yard?
45 bags of 80 lb mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix. Each 80 lb bag yields about 0.6 cubic feet.
How many tons is a cubic yard of gravel?
Typically 1.2 to 1.45 tons per cubic yard depending on the material: pea gravel about 1.2, crushed stone about 1.35, dense-graded base about 1.45. Confirm with your quarry, since they sell by weight.
What is soil swell and why does it matter?
Excavated soil expands 12-50% compared with its in-ground volume. If you plan haul-away using hole volume instead of swelled volume, you'll under-order trucks and skips by roughly a quarter.
What slope do I need for drainage?
The common minimums: 1% for drain pipes (1/8 inch per foot), 2% for patios and paved surfaces, and 5% for the ground surface within 10 feet of a foundation.
What size French drain do most yards need?
A 12-inch-wide, 18-24-inch-deep trench with 4-inch perforated pipe handles most residential yard drainage. Foundation drains and slope interceptors are deeper and should be designed case by case.
Can I use your results to get contractor quotes?
Yes - that's one of the best uses. Bringing dimensioned quantities to a contractor conversation helps you compare bids line by line and spot estimates that are far off the geometry.
Do you store my project data?
No. Calculations run entirely in your browser and are not sent to or stored on our servers. See our privacy policy for details.
When should I hire an engineer instead of using a calculator?
Anything structural (foundations, retaining walls, suspended slabs), excavation deeper than 5 feet, building on fill or expansive soil, chronic water intrusion, or visible movement in existing structures. Calculators plan materials; engineers design solutions.
Do your tools work in metric?
The tools currently use US units (feet, inches, cubic yards, tons). Metric support is planned. The documented formulas work in any unit system if you keep units consistent.