How Much Concrete for a 20x14 Foundation at 8" Thick?

How Much Concrete for a 20x14 Foundation at 8" Thick?

If you are planning to pour a 20x14 foundation, getting the right amount of concrete is critical. Order too little and you risk a cold joint; order too much and you waste money. This guide provides exact quantities, cost estimates, and pro tips for 2026.

Quick Answer

For a 20x14 foundation at 8" thick, you need approximately 7.60 cubic yards (including 10% waste). Order 7.75 yd3 from your supplier.

Step-by-Step Volume Calculation

Step 1: Convert thickness: 8 inches / 12 = 0.67 feet.

Step 2: Volume in cubic feet: 20 ft x 14 ft x 0.67 ft = 186.7 cubic feet.

Step 3: Convert to cubic yards: 186.7 / 27 = 6.91 cubic yards.

Waste Factor

Always order 10% extra for spillage and uneven ground: 6.91 yd3 x 1.10 = 7.60 yd3. Round up to 7.75 yd3 for ordering.

Bag Mix Option

• 80-lb bags (0.60 ft3 each): 312 bags at ~$6.50 = $2,184
• 60-lb bags (0.45 ft3 each): 415 bags at ~$5.00 = $2,075

2026 Cost Estimate (Southeast, 4000 PSI)

Item	Qty	Unit	Total
Ready-mix	7.60 yd3	$155/yd3	$1,178
80-lb bags	312	$6.50	$2,184
Rebar/mesh	280 ft2	$0.75	$210
Form lumber	--	--	$84
Vapor barrier	280 ft2	$0.10	$28

DIY: ~$1,472. Pro: $2,240-$5,040.

DIY vs Professional

Manageable DIY project with 2 helper(s) and mixer rental.

Reinforcement

Use wire mesh or #3 rebar at 18-inch centers. Adds ~$210 but dramatically extends lifespan. Must meet local codes; requires engineer's stamp.

Recommended PSI

For foundations: 4,000-5,000 PSI for structural and commercial loads.

FAQ

How long to cure?

70% strength at 7 days, full at 28. Walk after 24-48 hours; no heavy loads for one week.

Permit needed?

At 280 sq ft, you may need a permit ($50-200).

Uneven ground?

Excavate to consistent depth and add 4 inches compacted gravel. Prevents settling cracks.

Cold weather pouring?

Ideal: 50-90F. Below 40F, hydration slows. Below freezing, water expands before concrete sets. Use insulating blankets if needed.

Preparation Checklist Before You Pour

Before ordering concrete for your 20x14 foundation, make sure you have completed these steps:

1. Call 811 (Call Before You Dig) — Have underground utilities marked at least 3 business days before excavation.
2. Excavate to proper depth — Remove topsoil and organic material. Dig 12 inches deep to allow for 4 inches of gravel base plus 8 inches of concrete.
3. Compact the subbase — Add 4 inches of crushed gravel (ABC or 3/4-inch minus) and compact with a plate compactor. Proper compaction prevents 90% of cracking issues.
4. Build forms — Use 2x10 lumber for straight runs. Stake forms every 2-3 feet and ensure they are level with a string line or laser level. Forms should be braced against the weight of wet concrete.
5. Install reinforcement — Place wire mesh or rebar on chairs (dobie blocks) so it sits in the middle of the slab, not on the ground. Rebar should be tied at intersections.
6. Schedule delivery — Ready-mix concrete has a 90-minute window from truck to pour. Have 2-3 helpers lined up, a wheelbarrow, and a flat shovel ready.

Weather Considerations

Ideal pouring temperature is between 50F and 85F. Avoid pouring in rain, as excess water weakens the surface and can cause scaling. In hot weather (above 85F), start early in the morning and use cold-mix water. In cold weather (below 50F), use insulating blankets and consider ordering concrete with accelerators.

Check the 5-day forecast before scheduling. A sudden freeze within 24 hours of pouring can destroy a slab. Rain within the first 4-6 hours can ruin the surface finish.

Cost Comparison by Region

Concrete prices vary significantly depending on where you live. Here is a regional breakdown for a 20x14 slab at 8" thick (7.60 yd3 with waste):

Region	Price/yd3	Material Cost
Northeast	$195	$1,482
Southeast	$155	$1,178
Midwest	$160	$1,216
West Coast	$205	$1,558

These are 2026 material-only costs. Labor adds $3-$8 per square foot depending on region and complexity.

When to Choose Ready-Mix vs Bag Mix

For 7.60 cubic yards, ready-mix delivery is strongly recommended. Your order fits within a standard truck delivery.

Choose Ready-Mix When: You need 1.5+ yards, have truck access, and can pour within 90 minutes.

Choose Bag Mix When: The site is inaccessible to trucks, you need less than 1 yard, or you want to spread the work over multiple days.

Maintenance and Sealing

After your 20x14 foundation cures (28 days), apply a penetrating concrete sealer to protect against moisture, salt, and UV damage. Reapply every 2-3 years for driveways and every 3-5 years for patios. Sealing costs approximately $0.25-$0.50 per square foot — roughly $98 for your 280 sq ft slab.