Why Concrete Suppliers Don't Speak Feet — And What to Say When You Call

A concrete yard calculator translates the number you have (dimensions in feet) into the number your supplier needs (cubic yards). That translation — and the 10% overage you forget to add — is where most first-time concrete buyers make their most expensive mistake.

You measured in feet. The truck is loaded in yards. The gap between those two units has caused more short pours, botched orders, and emergency second deliveries than any other single point of failure in concrete work.

What a Cubic Yard Actually Is

One cubic yard equals 27 cubic feet. That's a cube 3 feet on every side: 3 × 3 × 3 = 27.

Visualize it this way: a standard interior door is roughly 80 inches tall and 32 inches wide. A cubic yard of concrete stacked against that door would fill it floor to ceiling and extend about 14 inches out from the wall. That's how much material you're talking about per yard — and it weighs approximately 4,000 pounds when wet.

Cured concrete settles to roughly 3,600 pounds per cubic yard. A standard readymix truck carries 8 to 10 cubic yards. That's 32,000 to 40,000 pounds of material before you add the truck's own weight.

The weight fact matters operationally: know where the truck can and cannot go before it arrives. A fully loaded concrete truck on soft or unprepared ground causes a different problem than running short on material.

The Formula That Does the Translation

Cubic yards = (length × width × (depth ÷ 12)) ÷ 27

The depth divides by 12 to convert inches to feet. The result divides by 27 to convert cubic feet to cubic yards.

1 cubic yard = 60 60-pound bags = 45 80-pound bags

Those bag equivalents come from the yield per bag: each 60-pound bag produces approximately 0.45 cubic feet of mixed concrete; each 80-pound bag produces approximately 0.60 cubic feet. Divide 27 by each figure and you get 60 and 45.

The Numbers — Common Sizes in Cubic Yards at 4-Inch Thickness

The overage column is what you say to the supplier. Not the base figure — the overage figure. That extra 10% covers subgrade irregularities, spillage, and the fact that your forms are never perfectly uniform. The overage cost is always less than the cost of running short.

A 20×40 driveway at 4 inches is a 10.87-yard order. That's a full truck from most suppliers. Below 5 to 8 yards, depending on your supplier, you'll likely pay a short load fee — an additional charge of $50 to $150 added because the truck isn't at capacity.

Convert your dimensions to cubic yards instantly →

The Short Load Fee — What It Is and When It Hits

Readymix suppliers set minimum profitable loads, typically 5 to 8 cubic yards. Ordering below that threshold triggers a short load fee. The fee compensates the supplier for dispatching a truck that isn't carrying a full load.

The fee ranges from $50 to $150 depending on the supplier and the region. On a 2-yard project ordered at $150 per yard, a $150 short load fee adds $75 per yard to your effective cost — nearly doubling the rate.

This is why the bags-vs-readymix comparison for small pads requires an honest fee calculation. The per-yard rate from the supplier is not the total per-yard cost if you're under their minimum.

How to Call a Supplier: The Sequence

Having your cubic yard figure before calling is the entire point of the calculation. The call itself is short:

1. Give your cubic yard figure with overage already added
2. Confirm their per-yard price for your project date
3. Ask about delivery fee, minimum order, and short load fee
4. Confirm pour date and delivery window

Suppliers appreciate buyers who already have their numbers. It shortens the call, reduces errors, and signals that you've done the planning work.

Frequently Asked Questions

How do you convert concrete measurements to cubic yards?

Multiply length by width to get square footage, then multiply by the depth in feet (divide inches by 12 to get feet), then divide by 27. For a 20×20 slab at 4 inches: 20 × 20 × 0.333 = 133.33 cubic feet ÷ 27 = 4.94 cubic yards. Add 10% and order 5.43 yards.

How many cubic yards of concrete do I need for a 20×20 slab?

A 20×20 slab at 4 inches thick requires 4.94 cubic yards. With the standard 10% overage, the order is 5.43 cubic yards. At 6 inches thick, the same footprint requires 7.41 cubic yards, ordering 8.15 yards. The thickness decision drives the volume figure more than the footprint does on larger slabs.

Should I order more concrete than I calculated?

Always. The industry standard is 10% overage above your calculated volume. Short pours mid-job require emergency material at premium prices, or force you to stop a pour while concrete already in the forms begins to cure — creating a cold joint. The 10% buffer on a 5-yard job is 0.5 yards, roughly $75 in material. That's a small insurance cost.

What is a short load fee for concrete?

A short load fee is a surcharge from readymix suppliers when your order falls below their minimum, typically 5 to 8 cubic yards. The fee runs $50 to $150 and applies regardless of how much you're ordering below the minimum. For small projects near that threshold, compare the full cost including the fee against the cost of handling the job with bags.

How does compounding depth and area affect cubic yard calculations?

Both variables multiply the volume linearly. Doubling the area doubles the yards needed. Doubling the thickness also doubles the yards. On a 10×10 slab, moving from 4 to 8 inches takes the order from 1.36 yards to 2.72 yards. On a 20×40 slab, the same thickness change moves the order from 10.87 yards to 21.78 yards. Thickness decisions on large projects have outsized material consequences.