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This barndominium slab concrete calculator turns your building size into cubic yards, a range of truckloads and a material cost. You supply the one number we cannot know, your supplier's price per cubic yard. It is built for East Texas builds around Tyler, where the soil changes how slabs are designed.
It is a planning estimate, not a quote. Your engineer's foundation plan sets the real thickness and beams.
En español: Calculadora de concreto para la losa de un barndominium en el este de Texas
| Line | Cubic yards |
|---|
The math behind the number
Concrete is sold by the cubic yard, which is 27 cubic feet. Convert thickness to feet (inches ÷ 12), multiply by length and width, then divide by 27. Here is that arithmetic for three slab sizes before any beams or extra.
| Slab size | 4 in | 5 in | 6 in |
|---|---|---|---|
| 30 × 40 ft | 14.8 | 18.5 | 22.2 |
| 40 × 60 ft | 29.6 | 37.0 | 44.4 |
| 50 × 80 ft | 49.4 | 61.7 | 74.1 |
Cubic yards, plain arithmetic. These are examples, not recommended thicknesses.
Why thickness matters so much: each extra inch on a 40 × 60 ft slab adds about 7.4 cubic yards, close to one more truck on an 8 cubic yard mixer. Ask your engineer before you trim thickness to save money.
Trucks and extra: what the industry says
- Truck size. The National Ready Mixed Concrete Association (NRMCA) says truck mixer capacity varies between 8 and 12 cubic yards. We show a range of loads for that reason.
- Extra to order. NRMCA says to order 4% to 10% more than an estimate from plan dimensions, to cover contingencies. It also says to avoid small clean-up loads.
- Source. NRMCA, CIP 31, Ordering Ready Mixed Concrete.
Why East Texas clay changes the slab
Clay-rich soil swells when wet and shrinks as it dries, so a slab can move unevenly, most at the edges. That is why an engineer may specify deeper perimeter beams, extra reinforcement or a post-tensioned design, and why those choices change your cubic yards. Our guide to barndominium foundations on East Texas clay shows what USDA soil data says for Smith County and what to ask before you pour.
Not engineering advice: use this tool to understand a bid, not to design a slab. Your engineer's plan sets the real thickness and beams, and a bid that says "slab included" without them is not comparable to one that does.
What the result leaves out
| Cost line | Why it is separate |
|---|---|
| Pad and fill | Priced by the dirt contractor, not the concrete supplier. |
| Rebar or cables | Set by the engineer's design. |
| Forming and finishing | Crew labor, quoted by the builder. |
| Pump, short-load and delivery fees | Vary by supplier and site access. |
Our budget line items guide lists where these appear in a full bid, and the barndominium cost calculator gives a whole-project range.
How to use the result with suppliers and builders
- Get the plan numbers
Ask for slab thickness, beam depth and width, and total slab area from the engineer's drawings.
- Get two or three prices per yard
Ask what is included: delivery, fuel, short-load fees, mix strength and any pumping.
- Run the calculator
Enter your plan numbers and each price. Compare the result with the concrete line in each bid.
- Ask about gaps
If a bid's slab is far from your number, ask what it includes. Use the form below to request quotes from independent local builders.
Before you sign, read how to choose a barndominium builder. We are a referral service that connects you with independent local builders; we do not pour concrete or give quotes ourselves.
Frequently asked questions
How many cubic yards of concrete does a barndominium slab need?
Multiply length, width and thickness (in feet) and divide by 27. A 40 by 60 ft slab at 4 inches is about 29.6 cubic yards before any extra for waste, beams or an uneven pad. Thicker slabs and deep perimeter beams add to that, and your engineer's plan sets both.
How much extra concrete should I order?
The National Ready Mixed Concrete Association says the quantity ordered should be 4% to 10% more than an estimate from the plan dimensions, to cover contingencies. A rough or over-dug pad usually pushes you toward the upper end. Your concrete supplier or crew can advise on your site.
How many trucks will my slab take?
The National Ready Mixed Concrete Association says truck mixer capacity varies from 8 to 12 cubic yards. The calculator divides your order by 8 and by 12 to give a range of loads. Your supplier will tell you what its trucks carry and how it schedules back-to-back loads.
Does this calculator price the whole slab?
No. It prices the concrete only, using the dollars per cubic yard from your own supplier quote. Pad prep, forming, rebar or post-tension cables, finishing, pumping, delivery or short-load fees and labor are separate lines on a builder's bid.
What thickness and beam size should I use?
Use the numbers on your engineer's foundation plan. The 4, 5 and 6 inch choices are only there so you can see how thickness changes the volume. On East Texas clay, the soil report and the engineer decide thickness, reinforcement and beams, not this page.
Where do I get a price per cubic yard?
Ask two or three local ready-mix suppliers, or ask your builder what price per yard is in the bid. Prices vary by mix strength, delivery distance and quantity, so we do not publish one.