Order of work
- Call 811 (in the US) a few days before digging so buried utilities are marked, and ask your town whether the slab needs a permit — many limit paved area or set distances from property lines.
- Lay out the slab with stakes and string 6 in outside every edge, and set the strings at the finished height with a slope of ¼ in per foot away from the house.
- Dig to the depth shown above, measured down from the strings, and compact the soil. Spread and compact the gravel base in 2–3 in layers until a boot heel barely marks it.
- Set the forms on edge with their tops on the string line, stake them every 3 ft and screw through the stakes; cut stakes off below the top of the form so the screed board can pass. A 2×4 is only 3½ in deep, so under a 4 in slab pack gravel against the bottom of the board on the outside. Against the house, fasten the expansion joint strip to the wall instead.
- Place the mesh or rebar on chairs at mid-depth, 3 in in from the forms. Lap mesh sheets one full square and tie laps and rebar crossings with wire.
- Pour: have helpers, wheelbarrows and tools ready before the truck arrives or the first bag is mixed. Dampen the base, fill the forms to slightly above the top, and screed with a straight 2×4 in a sawing motion along the forms.
- Finish: bull-float right after screeding, wait until the surface water has gone, then round the edges with an edger, groove the control joints ¼ of the slab deep (or saw-cut them within 6–18 hours), and give it a broom finish for grip.
- Cure: spray or roll on cure & seal as soon as the surface can’t be marked, or keep the slab wet under plastic for 7 days. Strip the forms after a day or two, backfill the edges, and keep heavy loads off for a week.
Tools you’ll need
- Plate compactor for the base (rental), shovels, a steel rake and wheelbarrows
- Mixer (rental) if you use bags; a concrete rake or come-along to spread
- Straight 2×4 screed board, bull float or magnesium float, edger and groover (or a saw for the joints)
- Stakes, mason’s line, line level and a 4 ft level; drill/driver, circular saw and a sledgehammer for the forms
- Bolt cutters for mesh or rebar, pliers and tie wire
- Stiff broom, garden sprayer or roller for cure & seal
- Waterproof gloves, rubber boots and safety glasses — wet concrete is caustic and burns skin
About this planner
Pouring a concrete patio, shed base or pad is one long day of work that depends on a week of planning: forms that won’t bulge, a compacted base, steel held at the right height, enough concrete on site before it starts to set, and joints in the right places so the slab cracks where you want it to. Most calculators stop at cubic yards. This planner works out the whole job from your slab’s size.
It lists every board, stake, bag or truckload, sheet of mesh or bar of rebar, and prices them with your local numbers. It also compares mixing bags yourself against ordering ready-mix and picks the cheaper, lays out the control joints, and gives the figures people forget: how deep to dig, how much slope to build in and how much soil to get rid of.
How to use it
- Enter the slab’s length, width and thickness. For an L-shape, plan each rectangle separately and add the lists.
- Set the gravel base depth and choose wire mesh, rebar or none.
- Say whether the slab is against the house: the wall then forms one side, and the list adds an expansion joint strip.
- Open Your local prices, enter your store’s bag price and a ready-mix quote, and let the planner pick bags or a truck. Print the project sheet to shop from.
How the quantities are worked out
Concrete = length × width × thickness × 1.10
Bags = concrete ÷ bag yield (80 lb = 0.60 cu ft, 60 lb = 0.45), rounded up
Ready-mix = concrete rounded up to the next ¼ cu yd; cost = yards × price + fees
Gravel = (length + 1 ft) × (width + 1 ft) × base depth × 1.15, at 1.5 tons per cu yd
Control joints: panels no longer than 2 × thickness (in) in feet, and at most 1.5 × as long as wide
Mesh sheets = (length − 6 in) × (width − 6 in) ÷ 42.75 sq ft
Rebar = bars 18 in apart each way, 3 in from the edges, + 10%, ÷ 20 ft
Chairs = one every 3 ft each way · Stakes = one every 3 ft per side + 1
Cure & seal = area ÷ 200 sq ft per gallon
Bag yields are from Quikrete’s data sheets. Control joints follow the Portland Cement Association’s rule of about 2 × the slab thickness in feet (8 ft for a 4 in slab), with panels kept close to square; the planner adds joints until both are true. A 5 × 10 ft mesh sheet lapped one 6 in square each way covers 4.5 × 9.5 = 42.75 sq ft. Chairs follow the Concrete Reinforcing Steel Institute’s 3 ft maximum spacing, and the cure & seal rate is the manufacturer’s 200 sq ft per gallon for curing. Ready-mix is compared at your price per yard plus the short-load and delivery fees your supplier quotes.
Worked example
These are the planner’s starting values and the results they produce:
| Slab length | 12 ft |
|---|---|
| Slab width | 12 ft |
| Thickness | 4 in |
| Gravel base | 4 in |
| Reinforcement | Wire mesh (5 × 10 ft sheets) |
| Next to the house? | Yes – a long side against the house |
| Concrete | Whichever is cheaper |
| Bag size | 80 lb bag (0.60 cu ft) |
| Curing | Cure & seal, sprayed or rolled on |
| Concrete mix, per bag | $6.50 |
| Ready-mix, per cu yd | $170.00 |
| Ready-mix short-load and delivery fees | $100.00 |
| Gravel base, per ton | $45.00 |
| Wire mesh, per 5 × 10 ft sheet | $14.00 |
| #3 rebar, per 20 ft bar | $11.00 |
| Rebar chairs, each | $0.25 |
| Form boards, per foot | $0.60 |
| Wood stakes, each | $0.75 |
| Expansion joint strip, per 10 ft | $8.00 |
| Cure & seal, per gallon | $30.00 |
| Bought | Item | Buy | Cost |
|---|---|---|---|
| Gravel base (crusher run)2.31 cu yd for 4 in compacted, 6 in past the open edges | 3.46 tons | $155.73 | |
| Form boards (2×4)38 ft for three sides; the house wall is the fourth | 1 × 14 ft, 2 × 12 ft | $22.80 | |
| Wood stakes (18–24 in)One every 3 ft and at each board end, plus 2½–3 in screws | 16 | $12.00 | |
| Expansion joint strip (½ in fiber)Isolation joint along 12 ft of house wall | 2 × 10 ft | $16.00 | |
| Wire mesh (6 × 6 in, 5 × 10 ft sheets)132 sq ft, sheets lapped 6 in; tie the laps | 4 sheets | $56.00 | |
| Rebar chairs (2 in)One every 3 ft each way, holding the steel at mid-depth | 25 | $6.25 | |
| Ready-mix concrete, delivered1.96 cu yd with 10% extra, rounded up to ¼ yd; incl. $100.00 fees | 2 cu yd | $440.00 | |
| Cure & seal compound200 sq ft per gallon as a curing coat | 1 gallon | $30.00 | |
| Estimated materials total | $738.78 | ||
Tips before you buy
- Get a ready-mix quote before buying bags. Above about a cubic yard the truck is usually cheaper, and it saves mixing 45 bags per yard by hand.
- Ask the supplier how far the truck’s chute reaches and check it can park that close without crossing a lawn, septic tank or soft ground. If it can’t, budget for a pump or plenty of wheelbarrows and helpers.
- Pour on a mild, overcast day if you can. Hot sun and wind dry the surface before you can finish it; don’t pour on frozen ground.
- Oil or spray the inside of the forms with form release so they come off clean.
- Driveways, garage floors, footings and slabs that carry a building need the thickness and reinforcement your local code or an engineer specifies; this planner lists materials, it doesn’t design structure.
Frequently asked questions
How many bags of concrete do I need for a 12×12 patio?
A 12 × 12 ft patio 4 in thick holds 48 cu ft of concrete; with 10% extra that’s 52.8 cu ft, or 88 bags of 80 lb mix (118 bags of 60 lb). That is 7,040 lb to haul and mix, so at typical prices a 2 cu yd ready-mix delivery is cheaper: about $440 with a $100 short-load fee, against $572 for the bags.
When is ready-mix cheaper than bags?
At $6.50 per 80 lb bag, $170 per cubic yard and a $100 short-load fee, the switch comes at about 1 cubic yard. An 8 × 8 ft slab 4 in thick is still cheaper in bags (40 bags, $260, against $270 for the smallest 1 yd truck), while a 9 × 8 ft slab is cheaper by truck (44 bags would cost $286). Enter your own prices and the planner picks for you.
How far apart should control joints be in a concrete patio?
About 2 times the slab thickness in feet: every 8 ft for a 4 in slab, 10 ft for 5 in, with panels as close to square as you can make them. A 12 × 12 ft patio gets one joint each way — four 6 × 6 ft panels and 24 ft of joints — grooved or cut 1 in deep, a quarter of the thickness.
Do I need rebar or wire mesh in a concrete patio?
Neither stops a slab from cracking — control joints decide where it cracks — but steel holds cracks tight so the pieces stay level. For a 12 × 12 ft patio you need 4 sheets of 5 × 10 ft mesh or 12 twenty-foot #3 bars in an 18 in grid, plus 25 chairs to hold either at mid-depth. Mesh is easier to handle; rebar is stiffer and easier to keep off the ground during the pour.
How deep do I dig for a concrete patio?
The slab thickness plus the gravel base: 4 in + 4 in = 8 in for a typical patio, and 6 in wider than the slab on the open sides so the forms sit on the base. For a 12 × 12 ft patio against the house that’s about 5 cu yd of soil to haul once it’s dug and loose.