How we calculate and check our numbers

Where our numbers come from

• Product data sheets. How much concrete a bag makes, how many square feet a gallon of paint covers, how many shingles are in a bundle: we take these from the manufacturer's technical data sheet, not from other calculators.
• Published prices, with a date. Default prices come from store listings and published price surveys, and each one shows where and when we saw it. They are only a starting point: every price field can be changed to your local price.
• Installation rules from the source. Rules like "bury one third of a fence post" come from the manufacturer's instructions. Building codes vary by city and county, so we point you to your local building department for anything structural.

How the calculators work

1. Exact volume or area first. Every project is broken into simple shapes (boxes, cylinders, steps) and measured in feet and inches, the way U.S. projects are.
2. Then the waste margin. We add 10% by default because forms bow, ground is uneven and some material is always lost. You can change it.
3. Then round up to what you can buy. Bags, boxes and bundles are rounded up to whole units. Ready-mix concrete is rounded up to the next 0.25 yd³.
4. Then the cost. Quantity × your price. We show material cost only; delivery, rentals and labor are extra.

Assumptions you should know

• Concrete bag yields are from the Quikrete Concrete Mix data sheet (an 80 lb bag makes about 0.6 ft³). Other brands are close but not identical: check the bag.
• Default prices: $6.47 for an 80 lb bag and $175 per cubic yard of ready-mix, the middle of the $160–$195 U.S. range for 2026. Short-load and delivery fees are not included.
• The bags-or-truck advice uses simple thresholds: bags up to 1 yd³, a truck from 3 yd³, and a comparison in between.
• Nominal lumber is converted to its real size (a 4×4 post measures 3.5 in).

How we test

All calculators share one measuring engine. Before any change goes live, automated tests check it against known results, such as "one cubic yard takes 45 bags of 80 lb" or "a 4-inch slab needs one cubic yard for every 81 square feet". Every table and example on our pages is calculated with that same engine, never typed by hand.

Updates and corrections

Each page shows its last update. We recheck prices and data sheets regularly and whenever a manufacturer changes a product. If you find an error, write to hello@yardacalc.com: we fix confirmed errors quickly and note the change date on the page.

What our calculators are not

They are estimates to help you plan and shop. They are not an engineering design, a contractor's bid or a code inspection. For footings, retaining walls, anything that carries a load and anything that needs a permit, follow your local code and a licensed professional.