What a 10x20 slab is for
A 10x20 slab is long and narrow. It fits a parking pad for a small trailer, a motorcycle or a lawn tractor, a 10x20 canopy carport, a side-yard path wide enough for a wheelbarrow both ways, or a long shed. At exactly 200 square feet, a shed on it is at the model code's permit-free limit.
Concrete for a 10x20 slab at 4, 5 and 6 inches
Every inch of thickness on a 10x20 slab is 16.7 cubic feet, or 0.62 cubic yards. The ready mix order and the bags in this table include 10 percent extra. Change the thickness or the extra in the calculator above.
| Thickness | Cubic feet | Cubic yards | Ready mix to order | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 66.7 | 2.47 | 2.72 cu yd | 123 | 163 |
| 5 in | 83.3 | 3.09 | 3.4 cu yd | 153 | 204 |
| 6 in | 100 | 3.7 | 4.07 cu yd | 184 | 245 |
The 4 inch row by hand: 20 × 10 × 0.333 = 66.7 cubic feet, and 66.7 ÷ 27 = 2.47 cubic yards. With 10 percent extra that is 73.3 cubic feet. An 80 lb bag makes 0.60 cubic feet and a 60 lb bag makes 0.45, so it takes 123 of one or 163 of the other.
Quikrete says a sidewalk should be at least 4 inches thick and small slabs normally run 4 to 6 inches, depending on the load. The concrete slab calculator page covers what the building code asks for.
Bags or a truck for a 10x20 slab
From bags, it is 123 bags of 80 lb mix at 4 inches, 9,840 lb to lift and mix, about $700 at McCoy's price of $5.99 a bag, or $5.69 for 42 or more.
From a truck, it is 2.72 cubic yards, about $299 to $408 at HomeAdvisor's $110 to $150 per cubic yard delivered. The National Ready Mixed Concrete Association says a truck mixer carries 8 to 12 cubic yards, so this is less than one truck load. HomeAdvisor says an order under a full truckload can carry a short-load fee of $40 to $60 per cubic yard, and suppliers often have a minimum order.
By these prices a 10x20 slab costs about $292 to $401 less from a truck than from bags, and it saves lifting 9,840 lb of mix. A short-load fee or a minimum order comes out of that gap, so get a delivered price for 2.72 cubic yards and compare it with $700. It is a bag job only if that quote comes in higher or a truck cannot reach the slab. The association notes that a loaded truck weighs about 80,000 lb and may not be able to cross loose dirt or a residential curb.
| Thickness | 80 lb bags | Bags weigh | Bags cost | Ready mix | Ready mix cost |
|---|---|---|---|---|---|
| 4 in | 123 | 9,840 lb | $700 | 2.72 cu yd, less than one truck load | $299 to $408 |
| 5 in | 153 | 12,240 lb | $871 | 3.4 cu yd, less than one truck load | $374 to $510 |
| 6 in | 184 | 14,720 lb | $1,047 | 4.07 cu yd, less than one truck load | $448 to $611 |
Prices are from the sources below, checked in October 2026; multiply the table by your own to compare. Gravel, steel, forms, finishing and labor are extra.
Pouring a 10x20 slab
The 10 foot width screeds in one pass with a 12 foot board, but the length means walking the board 20 feet down the forms, so work from one end and keep the concrete coming ahead of it. A truck chute or a wheelbarrow run along one long side reaches the whole slab.
Gravel base and slope
A 4 inch gravel base under a 10x20 slab is 66.7 cubic feet, or 2.47 cubic yards. Quikrete says to spread and compact 3 to 4 inches, and a 3 inch base is 50 cubic feet, or 1.85 cubic yards. Those are volumes of the finished layer. Gravel settles when it is compacted, so order a little more.
Outside, Quikrete says to slope the slab away from buildings and gives 1/4 inch per foot as the usual fall. Running across the 10 foot side, that is 2 1/2 inches from one edge to the other. Running along the 20 foot side, it is 5 inches. Set the forms to the slope, and the screed follows them.
Rebar or wire mesh
With bars 24 inches on center both ways, held 3 inches back from each edge, a 10x20 slab takes 6 bars 19 feet 6 inches long and 11 bars 9 feet 6 inches long. That is 222 feet of bar. With 10 percent extra, buy 13 bars 20 feet long. Every bar is shorter than the 20 foot length sold, so none has to be joined.
With wire mesh instead, 3 sheets 8 feet by 12.5 feet, lapped 8 inches, cover it. The spacing and the sheet size are where the calculator starts. Your plans or your building department set the steel for your slab.
Control joints
Quikrete says control joints in a 4 inch slab go every 6 to 8 feet and about a quarter of the slab deep, which is 1 inch. Keeping them no more than 8 feet apart cuts a 10x20 slab into 3 panels along the 20 foot side and 2 along the 10 foot side. That makes 6 panels, each 6 feet 8 inches by 5 feet, with 40 feet of joint to cut.
Before you pour a 10x20 slab
Twenty feet is too long to leave in one piece. Quikrete gives 10 feet as the most between control joints, and 6 to 8 feet for a 4 inch slab, so cut across it at least twice. As a parking pad for anything with an engine, ask your building department about thickness: the model code lets driveways go without a permit, but many towns set their own rules for them.
Other slab sizes
8x1010x1010x1212x1210x2012x2016x2020x2020x2424x2424x3030x40
Common questions
How much concrete do I need for a 10x20 slab?
A 10 by 20 foot slab 4 inches thick holds 66.7 cubic feet of concrete, which is 2.47 cubic yards. With 10 percent extra, order 2.72 cubic yards of ready mix. At 5 inches thick it holds 3.09 cubic yards and at 6 inches 3.7.
How many 80 lb bags of concrete do I need for a 10x20 slab?
123 bags at 4 inches thick, with 10 percent extra. They weigh 9,840 lb in all and cost about $700 at the store price checked in October 2026. At 5 inches thick it is 153 bags and at 6 inches 184.
How thick should a 10x20 concrete slab be?
Quikrete calls for at least 4 inches for a sidewalk and 4 to 6 inches for small slabs, depending on the load. The International Residential Code minimum for a house floor slab is 3.5 inches. On a 10x20 slab each extra inch adds 0.62 cubic yards, so going from 4 to 6 inches takes the ready mix order from 2.72 to 4.07 cubic yards. Ask your building department what it wants for a driveway or a garage floor.
Can you park a car on a 10x20 slab?
One car fits on it. A midsize sedan is about 16 feet long and 6 feet wide, so it leaves room to walk around the front and back but not much beside the doors. For regular parking, ask your town what thickness it wants for a driveway.
Does a shed on a 10x20 slab need a permit?
At exactly 200 square feet, a one-story detached shed is right at the limit in the model code, IRC R105.2, which lets sheds up to 200 square feet go without a building permit. A slab any bigger, or a town with a lower limit, puts it over the line.
Tools for this job
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- Form stakes. Hold the form boards in place while you pour.
- Concrete float. Smooths the surface after the concrete is leveled.
- Edger. Rounds the slab edges so they do not chip.
- Groover. Cuts control joints so cracks follow a straight line.
- Finishing trowel. Gives the slab its final smooth surface.
- Rubber boots. Keep wet concrete off your skin while you stand in the pour.
Sources
- Quikrete, Pouring and Finishing Concrete Slabs
- Quikrete, Concrete Sidewalks and Small Slabs project guide
- Quikrete Concrete Mix data sheet (yield per bag)
- National Ready Mixed Concrete Association, CIP 31: Ordering Ready Mixed Concrete
- International Residential Code 2021, Chapter 5: concrete floors on the ground (R506)
- International Residential Code 2021, Chapter 4: foundations (R403, concrete cover over steel)
- Wire Reinforcement Institute, Manual of Standard Practice: Structural Welded Wire Reinforcement
- City of Dubuque, Iowa, minimum requirements for a detached garage slab
- City of Fridley, Minnesota, Garage Slabs handout
- PJ's Rebar, stock rebar sizes and lengths
- International Residential Code 2021, Chapter 1: work exempt from permit (R105.2)
- McCoy's Building Supply: Quikrete Concrete Mix, 80 lb bag
- HomeAdvisor: concrete delivery cost, per cubic yard and short-load fees
Facts on this page were last checked against these sources in October 2026.