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Concrete Slab Calculator · Free calculator

10x12 Concrete Slab Calculator

A 10' × 12' slab covers 120 sq ft. At 4" thick that's 1.63 cubic yards of concrete with 10% waste — order 1.75 yd³ of ready-mix or 74 × 80 lb bags. Garage and RV pads at 6" need 2.44 yd³. Rebar, forms and base are worked out below.

Quick answer

4" slab (patio / shed)
1.63 yd³
80 lb bags @ 4"
74
6" slab (garage / RV)
2.44 yd³
Rebar #4 @ 18" OC
9 × 20' sticks
2x4 forms
4 × 16' boards
Est. cost @ 4" (ready-mix)
$289

▍Concrete Calculator

ft
in
ft
in
in
Waste Factor
$
L = 12' 0"W = 10' 0"D = 4"
Cubic Yards
1.63yd³
incl. 10% waste · Ready-mix truck: order 1.75 yd³
Cubic Feet
44.00ft³
Area
120.0sq ft
Weight
3.30tons
Weight
6,600lbs
Concrete bags needed
  • 80 lb bag (0.6 ft³ yield)74
  • 60 lb bag (0.45 ft³ yield)98
  • 40 lb bag (0.3 ft³ yield)147

Concrete for a 10x12 slab by thickness

120 sq ft, 10% waste included. Ready-mix ~$165/yd³ ordered in ¼ yd steps; 80 lb bags ~$6.50.

ThicknessTypical useCubic yardsOrder80 lb bags60 lb bagsWeightReady-mix80 lb bags $
4"Patio / Shed / Walkway1.63 yd³1.75 yd³74983.30 tons$289$481
5"Driveway / Hot tub pad2.04 yd³2.25 yd³921234.13 tons$371$598
6"Garage / RV Pad2.44 yd³2.50 yd³1101474.95 tons$413$715

Rebar grid for a 10x12 slab — 18" on center both ways

3" edge cover, no lap splices needed, 5% cut-off waste.

ItemQuantityNotes
Bars running the 12' way7 bars11' 6" each
Bars running the 10' way8 bars9' 6" each
Total rebar157 LFincl. laps
20 ft sticks to buy9+5% cut-off waste
Weight #3 / #459 / 105 lbs0.376 / 0.668 lb per ft
Wire ties56one per intersection
Rebar chairs (2"–3")16~36" grid
Alt: 6x6 welded wire mesh3 sheets5' × 10' sheets, 6" laps

Forms & site prep for 10x12

ItemQuantityNotes
Form perimeter44 LF2 × (10' + 12')
2x4 form boards (16 ft)4use 2x6 for 5"–6" slabs
Wood stakes (18"–24")20every 3 ft + each corner
Duplex nails402 per stake
Gravel base 4" (compacted)1.70 yd³ / 2.39 tons+15% for compaction
6-mil vapor barrier132 sq ft+10% for laps
Control joints10 LF1 cuts, panels ≤ 10'

How the math works

  1. Area: 12 ft × 10 ft = 120 sq ft
  2. Thickness in feet: 4" ÷ 12 = 0.333 ft
  3. Volume: 120 × 0.333 = 40.00 cu ft
  4. Add 10% waste: 40.00 × 1.10 = 44.00 cu ft
  5. Cubic yards: 44.00 ÷ 27 = 1.63 yd³ → order 1.75 yd³
  6. 80 lb bags: 44.00 ÷ 0.60 = 74 bags (60 lb: ÷ 0.45 = 98)
  7. Rebar: 7 bars × 11' 6" + 8 bars × 9' 6" = 157 LF → 9 sticks

Bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft (Quikrete / Sakrete). 1 yd³ = 45 × 80 lb bags.

Trade pro tips

  • 1.75 yd³ is under most plants' 4-yard minimum — ask about the short-load fee before ordering ready-mix.
  • Order 5–10% extra. Subgrade is never perfectly flat, and running short mid-pour leaves a cold joint.
  • Compact 4" of gravel base and slope the forms ¼" per foot away from any structure.
  • Chair the rebar so it sits in the middle third of the slab — rebar lying on the dirt does nothing.
  • Cut control joints ¼ of the slab depth, no more than 2–3 × the thickness (in feet) apart, within 6–18 hours.

Frequently asked questions

How many yards of concrete do I need for a 10x12 slab?

With 10% waste: 4" thick = 1.63 yd³ (order 1.75), 5" = 2.04 yd³ (order 2.25), 6" = 2.44 yd³ (order 2.50). A 10x12 slab is 120 sq ft.

How many 80 lb bags of concrete for a 10x12 slab 4 inches thick?

74 bags of 80 lb concrete (0.60 cu ft each) or 98 bags of 60 lb, including 10% waste. That is about 5,920 lbs of bags to haul.

How much rebar do I need for a 10x12 slab?

A grid at 18" on center both ways uses 7 bars running 12 ft and 8 bars running 10 ft — about 157 linear feet, or 9 twenty-foot sticks of #3 or #4 rebar, 56 ties and ~16 chairs.

How much does a 10x12 concrete slab cost?

Material only at 4": about $289 in ready-mix or $481 in 80 lb bags; at 6": about $413 ready-mix. Installed, 10x12 slabs typically run $6–$12 per sq ft ($720–$1,440) depending on region, access and finish.