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Concrete Slab Calculator · Free calculator

24x24 Concrete Slab Calculator

A 24' × 24' slab covers 576 sq ft. At 4" thick that's 7.82 cubic yards of concrete with 10% waste — order 8.00 yd³ of ready-mix or 352 × 80 lb bags. Garage and RV pads at 6" need 11.73 yd³. Rebar, forms and base are worked out below.

Quick answer

4" slab (patio / shed)
7.82 yd³
80 lb bags @ 4"
352
6" slab (garage / RV)
11.73 yd³
Rebar #4 @ 18" OC
43 × 20' sticks
2x4 forms
8 × 16' boards
Est. cost @ 4" (ready-mix)
$1,320

▍Concrete Calculator

ft
in
ft
in
in
Waste Factor
$
L = 24' 0"W = 24' 0"D = 4"
Cubic Yards
7.82yd³
incl. 10% waste · Ready-mix truck: order 8.00 yd³
Cubic Feet
211.20ft³
Area
576.0sq ft
Weight
15.84tons
Weight
31,680lbs
Concrete bags needed
  • 80 lb bag (0.6 ft³ yield)352
  • 60 lb bag (0.45 ft³ yield)470
  • 40 lb bag (0.3 ft³ yield)704

Concrete for a 24x24 slab by thickness

576 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 / Walkway7.82 yd³8.00 yd³35247015.84 tons$1,320$2,288
5"Driveway / Hot tub pad9.78 yd³10.00 yd³44058719.80 tons$1,650$2,860
6"Garage / RV Pad11.73 yd³11.75 yd³52870423.76 tons$1,939$3,432

Rebar grid for a 24x24 slab — 18" on center both ways

3" edge cover, 32 lap splices at 20" (40 bar diameters for #4), 5% cut-off waste.

ItemQuantityNotes
Bars running the 24' way16 bars23' 6" each
Bars running the 24' way16 bars23' 6" each
Total rebar805 LFincl. laps
20 ft sticks to buy43+5% cut-off waste
Weight #3 / #4303 / 538 lbs0.376 / 0.668 lb per ft
Wire ties256one per intersection
Rebar chairs (2"–3")64~36" grid
Alt: 6x6 welded wire mesh14 sheets5' × 10' sheets, 6" laps

Forms & site prep for 24x24

ItemQuantityNotes
Form perimeter96 LF2 × (24' + 24')
2x4 form boards (16 ft)8use 2x6 for 5"–6" slabs
Wood stakes (18"–24")36every 3 ft + each corner
Duplex nails722 per stake
Gravel base 4" (compacted)8.18 yd³ / 11.45 tons+15% for compaction
6-mil vapor barrier634 sq ft+10% for laps
Control joints96 LF4 cuts, panels ≤ 10'

How the math works

  1. Area: 24 ft × 24 ft = 576 sq ft
  2. Thickness in feet: 4" ÷ 12 = 0.333 ft
  3. Volume: 576 × 0.333 = 192.00 cu ft
  4. Add 10% waste: 192.00 × 1.10 = 211.20 cu ft
  5. Cubic yards: 211.20 ÷ 27 = 7.82 yd³ → order 8.00 yd³
  6. 80 lb bags: 211.20 ÷ 0.60 = 352 bags (60 lb: ÷ 0.45 = 470)
  7. Rebar: 16 bars × 23' 6" + 16 bars × 23' 6" = 805 LF → 43 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

  • 8.00 yd³ fits in one ready-mix truck — order by the ¼ yard and have the chute reach planned.
  • 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 24x24 slab?

With 10% waste: 4" thick = 7.82 yd³ (order 8.00), 5" = 9.78 yd³ (order 10.00), 6" = 11.73 yd³ (order 11.75). A 24x24 slab is 576 sq ft.

How many 80 lb bags of concrete for a 24x24 slab 4 inches thick?

352 bags of 80 lb concrete (0.60 cu ft each) or 470 bags of 60 lb, including 10% waste. That is about 28,160 lbs of bags to haul.

How much rebar do I need for a 24x24 slab?

A grid at 18" on center both ways uses 16 bars running 24 ft and 16 bars running 24 ft — about 805 linear feet, or 43 twenty-foot sticks of #3 or #4 rebar, 256 ties and ~64 chairs.

How much does a 24x24 concrete slab cost?

Material only at 4": about $1,320 in ready-mix or $2,288 in 80 lb bags; at 6": about $1,939 ready-mix. Installed, 24x24 slabs typically run $6–$12 per sq ft ($3,456–$6,912) depending on region, access and finish.