How much concrete for a 20x24 garage footing (12 x 8 in)?

Data checked October 2026

Short answer

88 ft of 12 × 8 in footing takes 2.17 cubic yards of concrete — 108 × 80-lb bags with 10% extra, or 2.5 yd³ of ready-mix.

Per foot: 12 × 8 in ÷ 144 = 0.667 cu ft; × 88 ft = 58.7 cu ft (2.17 yd³).
Bags with 10% extra: 108 × 80 lb or 144 × 60 lb — 8,640 lb to move (2.6 pallets).
Cost: about $640 in bags vs. $740 for 2.5 yd³ delivered — bags are cheaper here, but that is a lot of mixing.
Rebar: 2 continuous #4 bars need 10 × 20 ft sticks (194 ft with laps, 129 lb), held 3 in off the soil.
Under an 8 in wall the footing projects 2 in each side — the IRC wants 2 in to 8 in (the footing thickness).
A 20×24 ft garage has an 88 ft perimeter; 12 × 8 in under an 8 in block wall leaves a 2 in projection each side, the IRC minimum.

Adjust it to your exact job

Footing type

What are you pouring?

Size

Total length of footing

Add every run. For a closed rectangle use the perimeter: a 20×20 garage is 80 ft.

Width × thickness

Width

= 1'

Thickness

= 8"

Wall on top0 = skip

= 8"

#4 bars, continuous

You need

108× 80-lb bags

2.39 yd³ of concrete for 88 ft of 12 × 8 in footing, including 10% extra · 8,640 lb of bags

Concrete volume: 2.17yd³58.7 ft³ before waste
Per foot of footing: 0.67ft³1.11 × 80-lb bags
Ready-mix order: 2.5yd³quarter-yard steps, 1 yd minimum
#4 rebar: 10× 20 ft129 lb incl. laps

Code check (IRC 2021)

Width 12 in, thickness 8 in — meets the ruleIRC R403.1.1: at least 12 in wide and 6 in thick; soft soil or more stories need wider (Table R403.1(1)).
Projection 2 in each side — meets the ruleR403.1.1: at least 2 in past the wall face, and no more than the footing thickness.

Other bag sizes

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	216	—
50 lb · 0.375 ft³	173	—
60 lb · 0.45 ft³	144	$698
80 lb · 0.6 ft³	108	$640

Bags or a ready-mix truck?

108 bags

$640

Cheaper ✓ · materials only, before tax

2.5 yd³ delivered

$740

incl. short-load & delivery fees

At these prices a truck becomes cheaper from about 3.25 yd³ (147 bags). Over 1–2 yd³, a truck also saves hours of mixing: plan on 3–4 minutes per bag in a mixer.

That's 4.3 tons of bags — more than most pickups can carry in one trip. Ask about store delivery.

How deep?

The bottom of every exterior footing must sit at least 12 in below undisturbed ground (IRC R403.1.4) and below your local frost depth, which the building department sets. Dig to firm, undisturbed soil — never pour on loose fill.

Rebar placement

Hold bars 3 in off the soil on chairs or concrete blocks (IRC R403.1.3.5.3) and overlap splices. The IRC only mandates footing bars in Seismic Design Categories D0–D2; elsewhere follow your plans or engineer.

Timeline for standard 4000 psi mix

Walk on: 24 hours
Light loads / posts: 24 hours
Keep moist (cure): 5 days ≥70°F · 7 days at 50–70°F
Protect from freezing: 48 hours

Shopping list

108 bags Standard 4000 psi mix — 80-lb bags$640
10 sticks #4 rebar, 20 ft sticks (2 continuous bars)194 ft incl. 10% for laps · 129 lb$102
122 gal Clean water for mixing81–122 gal; start low, never exceed the max

Estimated total$742

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
108 bags × $Pallet price applied (42+ bags)
$640
#4 rebar, 20 ft
10 sticks × $
$102

Materials total$742

Typical U.S. prices checked October 2026. Tap any price to enter your store's.

Did this answer your question?

Compare

88 ft of footing at other sizes

Size	Cubic yards	80-lb bags	60-lb bags	Bag cost	Ready-mix
12 × 6 in	1.63	81	108	$480	$655
12 × 8 in	2.17	108	144	$640	$740
16 × 8 in	2.9	144	192	$854	$868
20 × 10 in	4.53	225	299	$1,334	$1,045
24 × 12 in	6.52	323	431	$1,915	$1,428

How this was worked out

12 in × 8 in = 96 sq in of cross-section, ÷ 144 = 0.667 cu ft per foot. Times 88 ft = 58.67 cu ft, ÷ 27 = 2.173 yd³.

With 10% extra that is 64.53 cu ft ÷ 0.6 cu ft per 80-lb bag = 107.6, rounded up to 108 bags.

At about $170 per yard plus delivery, fuel and a short-load fee under 4 yd³, a truck beats bags from roughly 3.25 yd³. This job is 2.39 yd³ with waste, so bags make sense — if you have the crew to mix them.

The full method, material data and tips are on the main concrete footing calculator page.

Similar jobs

Other sizes people check

Sources

Data behind this answer

Quikrete Concrete Mix No. 1101 — technical data sheet — bag yields (80 lb = 0.60 cu ft, 60 lb = 0.45, 50 lb = 0.375, 40 lb = 0.30), water per bag, curing times; post method: 6 in of dry mix in the hole bottom, 24 h before strain · checked October 2026
Sakrete High-Strength Concrete Mix — TDS — same yields per bag weight; Sakrete recommends +10% overage · checked October 2026
Home Depot & Lowe's listings — Quikrete 80 lb Concrete Mix — $5.98–$6.98 per 80-lb bag; $5.93 bulk tier at 42+ bags; 42 bags per pallet; Fast-Setting 50 lb $7.97 · checked October 2026
Ernest Maier — #3 and #4 steel rebar listings — #4 $0.51/ft and #3 $0.31/ft, sold in 20 ft lengths (2026) · checked October 2026
Published 2026 ready-mix plant price sheets (e.g. Gehring Concrete) — $146–$285 per yd³ before fees; short-load fees $50–$200 · checked October 2026
BLS Producer Price Index — ready-mix concrete (via FRED) — +2.3% Sept 2025 → Sept 2026 · checked October 2026
International Residential Code 2021 — R403.1 footings & Table R403.1(1) — 12 × 6 in minimum footing, width by soil bearing, 12 in below undisturbed ground, 3 in cover over bars cast against earth; deck footings R507.3 · checked October 2026

Short answer

88 ft of 12 × 8 in footing takes 2.17 cubic yards of concrete — 108 × 80-lb bags with 10% extra, or 2.5 yd³ of ready-mix.

Per foot: 12 × 8 in ÷ 144 = 0.667 cu ft; × 88 ft = 58.7 cu ft (2.17 yd³).

Bags with 10% extra: 108 × 80 lb or 144 × 60 lb — 8,640 lb to move (2.6 pallets).

Cost: about $640 in bags vs. $740 for 2.5 yd³ delivered — bags are cheaper here, but that is a lot of mixing.

Rebar: 2 continuous #4 bars need 10 × 20 ft sticks (194 ft with laps, 129 lb), held 3 in off the soil.

Under an 8 in wall the footing projects 2 in each side — the IRC wants 2 in to 8 in (the footing thickness).

A 20×24 ft garage has an 88 ft perimeter; 12 × 8 in under an 8 in block wall leaves a 2 in projection each side, the IRC minimum.

Adjust it to your exact job

Footing type

What are you pouring?

Size

Total length of footing

Add every run. For a closed rectangle use the perimeter: a 20×20 garage is 80 ft.

Width × thickness

Width

= 1'

Thickness

= 8"

Wall on top0 = skip

= 8"

#4 bars, continuous

You need

108× 80-lb bags

2.39 yd³ of concrete for 88 ft of 12 × 8 in footing, including 10% extra · 8,640 lb of bags

Concrete volume: 2.17yd³58.7 ft³ before waste
Per foot of footing: 0.67ft³1.11 × 80-lb bags
Ready-mix order: 2.5yd³quarter-yard steps, 1 yd minimum
#4 rebar: 10× 20 ft129 lb incl. laps

Code check (IRC 2021)

Width 12 in, thickness 8 in — meets the ruleIRC R403.1.1: at least 12 in wide and 6 in thick; soft soil or more stories need wider (Table R403.1(1)).
Projection 2 in each side — meets the ruleR403.1.1: at least 2 in past the wall face, and no more than the footing thickness.

Other bag sizes

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	216	—
50 lb · 0.375 ft³	173	—
60 lb · 0.45 ft³	144	$698
80 lb · 0.6 ft³	108	$640

Bags or a ready-mix truck?

108 bags

$640

Cheaper ✓ · materials only, before tax

2.5 yd³ delivered

$740

incl. short-load & delivery fees

At these prices a truck becomes cheaper from about 3.25 yd³ (147 bags). Over 1–2 yd³, a truck also saves hours of mixing: plan on 3–4 minutes per bag in a mixer.

That's 4.3 tons of bags — more than most pickups can carry in one trip. Ask about store delivery.

How deep?

Rebar placement

Timeline for standard 4000 psi mix

Walk on: 24 hours
Light loads / posts: 24 hours
Keep moist (cure): 5 days ≥70°F · 7 days at 50–70°F
Protect from freezing: 48 hours

Shopping list

108 bags Standard 4000 psi mix — 80-lb bags$640
10 sticks #4 rebar, 20 ft sticks (2 continuous bars)194 ft incl. 10% for laps · 129 lb$102
122 gal Clean water for mixing81–122 gal; start low, never exceed the max

Estimated total$742

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
108 bags × $Pallet price applied (42+ bags)
$640
#4 rebar, 20 ft
10 sticks × $
$102

Materials total$742

Typical U.S. prices checked October 2026. Tap any price to enter your store's.

Size

Cubic yards

80-lb bags

60-lb bags

Bag cost

Ready-mix

12 × 6 in

1.63

108

$480

$655

12 × 8 in

2.17

108

144

$640

$740

16 × 8 in

2.9

144

192

$854

$868

20 × 10 in

4.53

225

299

$1,334

$1,045

24 × 12 in

6.52

323

431

$1,915

$1,428

How this was worked out

12 in × 8 in = 96 sq in of cross-section, ÷ 144 = 0.667 cu ft per foot. Times 88 ft = 58.67 cu ft, ÷ 27 = 2.173 yd³.

With 10% extra that is 64.53 cu ft ÷ 0.6 cu ft per 80-lb bag = 107.6, rounded up to 108 bags.

The full method, material data and tips are on the main concrete footing calculator page.