Site information
How our numbers are produced
Every result on this site comes from one of two kinds of number, and we keep them separate on purpose. Published figures come from industry references and manufacturer data, and we do not change them. Planning assumptions are our own defaults for things that vary by market, and every one of them is editable inside the calculator.
Published figures we do not invent
These are fixed by geometry, physics or the manufacturer, and they are what the formulas rest on.
| Figure | Value | Where it comes from |
|---|---|---|
| Cubic yard | 27 cubic feet | Definition |
| Cubic meter | 1.30795 cubic yards | Definition |
| Cured normal weight concrete | 150 lb per cubic foot | Portland Cement Association and ready mix industry references |
| Bag yields | 80 lb = 0.60 cu ft, 60 lb = 0.45, 50 lb = 0.375, 40 lb = 0.30 | Coverage printed on the manufacturer bag |
| Blocks per square foot | 1.125 for a nominal 8 by 16 in face | 144 sq in per sq ft divided by the 128 sq in block face |
| Mortar coverage | One 80 lb bag per 33 standard blocks | Masonry industry rule of thumb, matches bag coverage |
| Rebar weight | #4 = 0.668 lb/ft, #5 = 1.043 lb/ft | Standard bar schedules |
| Control joint spacing | About 30 times slab thickness, capped near 15 ft | PCA guidance for slabs on grade |
Planning assumptions we set and review
These are national planning figures. They are the honest middle of a wide field, not a quote for your zip code, and the calculator lets you replace each one.
| Assumption | Default | Basis | Last reviewed |
|---|---|---|---|
| Ready mix concrete | $165 per cubic yard | National average for 3,500 psi delivered mix | August 31, 2026 |
| Crushed stone base | $45 per cubic yard | National average delivered | August 31, 2026 |
| Placing labor | $4.50 per square foot | Form, pour and broom finish | August 31, 2026 |
| Wire mesh | $0.35 per square foot | Material and placement | August 31, 2026 |
| Rebar grid at 18 in on center | $1.10 per square foot | Material and placement | August 31, 2026 |
| Vapor barrier | $0.50 per square foot | 10 mil poly, installed | August 31, 2026 |
| Pump or buggy | $650 per day | Trailer pump or buggy crew, one day | August 31, 2026 |
| Finish adders over broom | Smooth $0.50, exposed $2.00, stamped $8.00 per sq ft | Typical spread between finishes | August 31, 2026 |
| Floor finish adders | Seal $0.75, stain $4.00, polish $6.00 per sq ft | Basic single color work | August 31, 2026 |
| Cost range | 12 percent under to 18 percent over | How far honest quotes spread on the same scope | August 31, 2026 |
Prices are reviewed quarterly. When a default changes, the change is listed in the page changelog and the review date in this table moves with it.
How a formula gets published here
- The figure has to exist in a published industry or manufacturer source, not in someone's memory.
- The formula is written out in words on the calculator page, so a reader can follow it without the tool.
- A worked example with real numbers is calculated by hand and must match what the calculator returns.
- The example is covered by an automated test that runs on every build. If the test fails, the site does not publish.
Two of those hand checks are the site's ground truth: a 40 by 8 ft wall with one 9 by 7 ft opening and 5 percent waste returns 304 blocks, and a 20 by 20 ft slab at 4 inches returns 4.94 cubic yards before waste and 5.43 after 10 percent.
What we do not do
We do not quote your job, and we are not engineers. Structural thickness, reinforcement design, soil bearing and frost protection belong to your local building department and, where loads matter, a licensed engineer. We also do not accept payment to change a default price or to feature a supplier.
Every default listed above is editable inside the tool that uses it. Open the concrete slab cost calculator to replace the ready mix price and finish adders with your own quote, the concrete pad cost calculator for a shed or equipment base, the concrete floor cost calculator for interior work, or the concrete block calculator for wall material. For volume alone, without any pricing, use the concrete calculator.
Delivered prices and the fees that sit on top of them are broken down further in the concrete price per yard guide.
Every figure on this page carries the date it was last reviewed, and the author profile explains who checks them and how often.