You have measured the space for a shed or garage, but the concrete quote is still hard to judge. The slab thickness, ground preparation and finish need to be beside the price.
So Mike Day, a concrete contractor in Maine, publishes base slab estimates of $12 per square foot for 4-inch concrete and $12.50 for 6-inch concrete. Excavation and subbase are separate.
I checked his published 2025 prices on October 22, 2026. I will show the size calculation, compare his different slab packages and explain what the homeowner examples actually included.
Base Slab Prices by Size
Day’s general slab estimate includes forming, concrete placement, finishing and other stated slab components. It does not turn an unprepared site into a building-ready lot.
For the first example, 20 x 20 = 400 square feet. Applying Day’s six-inch rate gives 400 x $12.50 = $5,000. That is a calculation of the slab work, before separate ground preparation.
For a rectangular pad, multiply length by width before applying the matching unit rate. A small job minimum, thickened edges or different finish can prevent the total from scaling evenly.
Why a Shed Pad Can Have Another Price
Day’s shed slab estimates use a simpler four-inch specification. Those prices exclude excavation and gravel; the work is different from his general slab package.
His shed page explains that a small slab still needs a crew visit, forms, placement and finishing. Ordering half the area does not automatically halve those tasks.
Do not read the two 20 x 20 examples as competing prices for identical work. The shed example and the six-inch base example differ in thickness and their described finishing scope.
What Owners Paid or Were Quoted
In September 2022, central Virginia member wildman163 posted a $30,000 quote for a 32 x 44-foot slab, footings, thickened edges, gravel, equipment and a pump allowance.
On November 14, the same owner reported finding a contractor for $12,500, including preparation to the same specifications. The follow-up describes an arranged job rather than an itemized paid invoice.
In that thread, North Alabama member hydrojim reported paying about $9,000 for 864 square feet of eight-inch concrete. The owner did the backfill, compaction, rebar and vapor barrier work.
That Alabama total leaves out substantial owner labor. It would be misleading to use it as a complete contractor price for preparing and building a slab from bare ground today.
Separate Concrete From the Installed Slab
A ready-mix price buys concrete by volume. A slab quote can also buy forms, reinforcement, placement, finishing and joints. My concrete price per yard guide covers the supply side.
The pictures here illustrate slab work. They do not show the residential jobs behind the quoted prices, and the reinforcement in a photograph is not a design for your site.
For a load-bearing garage or building foundation, get the required design and local approvals before choosing thickness or reinforcement. A cheap shed-pad specification should not become a substitute for that design.
What to Put on the Estimate
Have the contractor identify the finished dimensions, thickness, concrete specification, reinforcement and edge or footing details. Note who supplies the prepared base and who checks it before placement.
Then separate excavation, removal of old concrete, gravel, compaction, vapor barrier, insulation, pumping and access work. Ask which are included and which need another contractor.
The finish also matters to the comparison. Ask about the surface texture, slope, joint layout and curing work so that two similar totals describe a slab you can actually use for the same purpose.
Concrete Slab Cost Questions
How much is a 20 x 20 concrete slab?
Day’s published six-inch base example is $5,000, with prep separate. His simpler four-inch shed example is $2,560. Match the specification before using either figure.
Is excavation included in a per-square-foot price?
Day separates excavation and subbase from his base slab estimate. Other contractors can package the work differently, so the estimate needs to name the site preparation.
Can I calculate a slab from the concrete yard price?
That calculates one material component. Forms, placement, reinforcement, finishing and site work can still be needed, along with delivery or small-load charges.
Can I choose four inches just to reduce the price?
Choose a slab design for the building, loads, ground and local requirements. A shed example does not establish the right thickness or footing details for a garage or another structure.
Where These Slab Prices Come From
US contractor pages checked October 22, 2026. Day’s published estimates are for 2025; the owner reports are from 2022.
- Mike Day: base slab rates, inclusions and sizes
- Mike Day: four-inch shed slab packages
- Garage Journal: Virginia quotes and an Alabama paid example
I hope this helps you put the slab and its preparation on the same estimate. You can share a recent US quote at costcheckr@gmail.com.
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