How Much Does a 20x30 Concrete Slab Cost?
A 20x30 concrete slab costs $3,600–7,200 installed at $6–12 per square foot. At 600 square feet it's the footprint of an oversized two-car garage or a garage-plus-workshop, and it sits right at a logistics threshold: 8.15 cubic yards at 4 inches fits one ready-mix truck, but 10.19 yards at 5 inches usually needs two.
A 20x30 concrete slab costs $3,600–7,200 installed — 600 square feet at the typical $6–12 per square foot. Where you land depends mostly on thickness, reinforcement, and your local labor rate. For your exact numbers, use the concrete cost calculator.
What a 20x30 Slab Is Usually For
Twenty by thirty is the step up from a basic two-car garage. The extra 10 feet of depth gives room for a workbench, storage wall, or a longer truck. Common uses:
- Oversized two-car garage — full-size pickup plus a car, with storage at the back.
- Garage with a workshop bay — tools and a bench along one side.
- Small detached shop or hobby barn.
Because most of these carry vehicles and point loads from equipment, a 20x30 is more often poured at 5 inches than a patio of similar size would be. See the garage floor thickness guide for thickness by use.
One Truck or Two
| Thickness | Cubic Yards (exact) | With 10% Waste | 80-lb Bags | Ready-Mix at $165–205/yd | Trucks (8–10 yd) |
|---|---|---|---|---|---|
| 4 in | 7.41 | 8.15 | 367 | $1,344–1,670 | 1 (full load) |
| 5 in | 9.26 | 10.19 | 459 | $1,681–2,088 | 2 |
| 6 in | 11.11 | 12.22 | 550 | $2,017–2,506 | 2 |
A standard ready-mix truck holds 8–10 cubic yards, so the 4-inch pour is one truck and anything thicker usually spills into a second. The second truck adds scheduling risk more than cost: if it's delayed, the first load starts setting and you get a cold joint. Ask your supplier to dispatch them back-to-back. The concrete cost per yard guide covers delivery fees and minimums.
20x30 Slab Cost in Four Cities
These ranges come from our slab foundation cost by city data at 600 square feet — the closest match for a garage or shop slab with a bearing edge:
| Metro | Installed $/sq ft | 20x30 Slab (600 sq ft) |
|---|---|---|
| Los Angeles, CA | $4.99–12.62 | $2,994–7,572 |
| Phoenix, AZ | $5.36–11.94 | $3,216–7,164 |
| Minneapolis, MN | $8.76–14.80 | $5,256–8,880 |
| Columbus, OH | $9.09–16.07 | $5,454–9,642 |
In frost climates like Minneapolis or Columbus, a detached garage also needs footings below the frost line, which a slab-only quote won't include. The foundation cost calculator prices stem wall and monolithic options by footprint.
Base, Rebar, and Joints
- Gravel base: 4 inches of compacted stone under 600 sq ft is 7.41 cubic yards — about 10.4 tons, $185–370 at $25–50 per yard.
- Rebar: #4 bar at 18 inches each way comes to about 840 linear feet ($630–1,260), plus laps on the 30-foot runs since stock bars are 20 feet long.
- Control joints: A 10-foot grid gives six 10x10 panels. Put a joint in line with the garage door opening edges if the layout allows — cracks like to start at re-entrant corners.
- Slope: Pitch the floor about 1/8 inch per foot toward the door so water from vehicles drains out.
DIY vs. Contractor for a 20x30 Slab
Materials for a 4-inch slab run roughly $2,160–3,300: ready-mix ($1,344–1,670), gravel ($185–370), and rebar ($630–1,260), before forms and a power-trowel rental. Against $3,600–7,200 installed the saving is real, but 600 square feet of garage floor is a professional-scale pour — a crew needs to place, screed, and finish a full truck (or two) in one window. Most homeowners at this size are better served getting three bids; see how to hire a concrete contractor.
Comparing sizes? The 20x20 slab cost covers a standard two-car garage, and the 30x30 slab cost a three-car garage or shop.