How much concrete for a 30x40 building footing (20 x 10 in)?

Data checked October 2026

Short answer

140 ft of 20 × 10 in footing takes 7.2 cubic yards of concrete — 357 × 80-lb bags with 10% extra, or 8 yd³ of ready-mix.

Per foot: 20 × 10 in ÷ 144 = 1.389 cu ft; × 140 ft = 194.4 cu ft (7.2 yd³).
Bags with 10% extra: 357 × 80 lb or 476 × 60 lb — 28,560 lb to move (8.5 pallets).
Cost: about $2,117 in bags vs. $1,555 for 8 yd³ delivered — the truck is cheaper here.
Rebar: 2 continuous #4 bars need 16 × 20 ft sticks (308 ft with laps, 206 lb), held 3 in off the soil.
Under an 8 in wall the footing projects 6 in each side — the IRC wants 2 in to 10 in (the footing thickness).
A 30×40 ft shop or house footprint has a 140 ft perimeter; 20 × 10 in leaves plenty of margin over the 12 × 6 in minimum for heavier loads or softer soil.

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' 8"

Thickness

= 10"

Wall on top0 = skip

= 8"

#4 bars, continuous

You need

357× 80-lb bags

7.92 yd³ of concrete for 140 ft of 20 × 10 in footing, including 10% extra · 28,560 lb of bags

Concrete volume: 7.2yd³194.4 ft³ before waste
Per foot of footing: 1.39ft³2.31 × 80-lb bags
Ready-mix order: 8yd³quarter-yard steps, 1 yd minimum
#4 rebar: 16× 20 ft206 lb incl. laps

Code check (IRC 2021)

Width 20 in, thickness 10 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 6 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	713	—
50 lb · 0.375 ft³	571	—
60 lb · 0.45 ft³	476	$2,309
80 lb · 0.6 ft³	357	$2,117

Bags or a ready-mix truck?

357 bags

$2,117

materials only, before tax

8 yd³ delivered

$1,555

Cheaper ✓ · incl. delivery & fuel

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 14.3 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

357 bags Standard 4000 psi mix — 80-lb bags$2,117
16 sticks #4 rebar, 20 ft sticks (2 continuous bars)308 ft incl. 10% for laps · 206 lb$163
402 gal Clean water for mixing268–402 gal; start low, never exceed the max

Estimated total$2,280

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
357 bags × $Pallet price applied (42+ bags)
$2,117
#4 rebar, 20 ft
16 sticks × $
$163

Materials total$2,280

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

Did this answer your question?

Compare

140 ft of footing at other sizes

Size	Cubic yards	80-lb bags	60-lb bags	Bag cost	Ready-mix
12 × 6 in	2.59	129	172	$765	$825
12 × 8 in	3.46	172	229	$1,020	$875
16 × 8 in	4.61	229	305	$1,358	$1,088
20 × 10 in	7.2	357	476	$2,117	$1,555
24 × 12 in	10.37	514	685	$3,048	$2,345

How this was worked out

20 in × 10 in = 200 sq in of cross-section, ÷ 144 = 1.389 cu ft per foot. Times 140 ft = 194.44 cu ft, ÷ 27 = 7.202 yd³.

With 10% extra that is 213.89 cu ft ÷ 0.6 cu ft per 80-lb bag = 356.5, rounded up to 357 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 7.92 yd³ with waste, so order ready-mix.

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

140 ft of 20 × 10 in footing takes 7.2 cubic yards of concrete — 357 × 80-lb bags with 10% extra, or 8 yd³ of ready-mix.

Per foot: 20 × 10 in ÷ 144 = 1.389 cu ft; × 140 ft = 194.4 cu ft (7.2 yd³).

Bags with 10% extra: 357 × 80 lb or 476 × 60 lb — 28,560 lb to move (8.5 pallets).

Cost: about $2,117 in bags vs. $1,555 for 8 yd³ delivered — the truck is cheaper here.

Rebar: 2 continuous #4 bars need 16 × 20 ft sticks (308 ft with laps, 206 lb), held 3 in off the soil.

Under an 8 in wall the footing projects 6 in each side — the IRC wants 2 in to 10 in (the footing thickness).

A 30×40 ft shop or house footprint has a 140 ft perimeter; 20 × 10 in leaves plenty of margin over the 12 × 6 in minimum for heavier loads or softer soil.

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' 8"

Thickness

= 10"

Wall on top0 = skip

= 8"

#4 bars, continuous

You need

357× 80-lb bags

7.92 yd³ of concrete for 140 ft of 20 × 10 in footing, including 10% extra · 28,560 lb of bags

Concrete volume: 7.2yd³194.4 ft³ before waste
Per foot of footing: 1.39ft³2.31 × 80-lb bags
Ready-mix order: 8yd³quarter-yard steps, 1 yd minimum
#4 rebar: 16× 20 ft206 lb incl. laps

Code check (IRC 2021)

Width 20 in, thickness 10 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 6 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	713	—
50 lb · 0.375 ft³	571	—
60 lb · 0.45 ft³	476	$2,309
80 lb · 0.6 ft³	357	$2,117

Bags or a ready-mix truck?

357 bags

$2,117

materials only, before tax

8 yd³ delivered

$1,555

Cheaper ✓ · incl. delivery & fuel

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 14.3 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

357 bags Standard 4000 psi mix — 80-lb bags$2,117
16 sticks #4 rebar, 20 ft sticks (2 continuous bars)308 ft incl. 10% for laps · 206 lb$163
402 gal Clean water for mixing268–402 gal; start low, never exceed the max

Estimated total$2,280

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
357 bags × $Pallet price applied (42+ bags)
$2,117
#4 rebar, 20 ft
16 sticks × $
$163

Materials total$2,280

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

2.59

129

172

$765

$825

12 × 8 in

3.46

172

229

$1,020

$875

16 × 8 in

4.61

229

305

$1,358

$1,088

20 × 10 in

7.2

357

476

$2,117

$1,555

24 × 12 in

10.37

514

685

$3,048

$2,345

How this was worked out

20 in × 10 in = 200 sq in of cross-section, ÷ 144 = 1.389 cu ft per foot. Times 140 ft = 194.44 cu ft, ÷ 27 = 7.202 yd³.

With 10% extra that is 213.89 cu ft ÷ 0.6 cu ft per 80-lb bag = 356.5, rounded up to 357 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 7.92 yd³ with waste, so order ready-mix.

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