How many 80 lb bags per cubic yard?

Approximately 45 bags of 80 lb concrete = 1 cubic yard. Each 80 lb bag yields ~0.60 ft³. Always add 10% waste.

When should I use bags vs. ready-mix?

Under 0.5 yd³ → bags are cheaper. Over 0.5 yd³ → ready-mix truck is more economical. Short-load fees apply under 8 yd³.

What PSI concrete for a driveway?

3000-4000 PSI with 4-6 inch thickness. Use 4000 PSI for heavy vehicle traffic. Always check local building codes.

Do I need rebar or wire mesh?

Wire mesh for patios/walkways (non-structural). Rebar (#3 or #4) for driveways, garage floors, structural slabs. 12-18 inch grid spacing.

What does a yard of concrete cost in 2026?

National average: $130-190/yd³ for 3000 PSI. Northeast/West Coast higher ($160-200). Southeast/Midwest lower ($120-150).

How thick should a concrete slab be?

Patios/walkways: 4 inches. Driveways: 5-6 inches. Garage floors: 5-6 inches. Commercial/heavy: 6-8 inches. Check local code.

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How to Estimate Concrete Yardage - Complete Guide | Concrete Yardage

Published on 2026-06-10

How to Estimate Concrete Yardage: The Complete Guide

Estimating concrete yardage is the single most important step in any concrete project. Order too little and you face cold joints and structural weakness. Order too much and you waste hundreds of dollars. This guide gives you the exact formula, real-world examples, and the common mistakes that trip up even experienced DIYers.

The Basic Formula

The formula for calculating concrete yardage is straightforward:

Cubic Yards = (Length x Width x Depth in feet) / 27

Here is why: concrete is sold by the cubic yard. There are 27 cubic feet in one cubic yard (3 ft x 3 ft x 3 ft). So you calculate the total volume in cubic feet, then divide by 27.

Step-by-Step: How to Estimate Concrete Yardage

Measure length and width in feet. For a 20x30 slab, that is 600 square feet.
Convert thickness to feet. A 4-inch slab = 4 / 12 = 0.33 feet. A 6-inch slab = 6 / 12 = 0.50 feet.
Multiply: Length x Width x Depth (in feet) = cubic feet.
Divide by 27 to get cubic yards.
Add 10% waste factor for spillage, uneven ground, and form irregularities.

Real-World Examples

Project	Dimensions	Thickness	Cubic Yards (raw)	With 10% Waste
10x10 Patio	10 x 10 ft	4 inches	1.23 yd³	1.35 yd³
12x12 Shed Base	12 x 12 ft	4 inches	1.78 yd³	1.96 yd³
20x30 Driveway	20 x 30 ft	6 inches	11.11 yd³	12.22 yd³
24x24 Garage	24 x 24 ft	6 inches	10.67 yd³	11.73 yd³
30x40 Workshop	30 x 40 ft	6 inches	22.22 yd³	24.44 yd³

Common Mistakes When Estimating Concrete

These are the errors that cost homeowners the most money:

Forgetting the waste factor. Always add 10%. On a 20x30 driveway, skipping waste means ordering 11.1 yards instead of 12.2 -- a full yard short.
Measuring thickness in inches without converting. If you multiply 20 x 30 x 6 (using inches directly), you get 3,600 / 27 = 133 yards. Absurdly wrong. Always convert inches to feet first.
Ignoring ground slope. If your site slopes 2 inches over 20 feet, measure at multiple points and use the average depth.
Not accounting for form thickness. A 2x6 form is actually 5.5 inches wide, not 6. This reduces internal volume slightly.

How Many Bags vs. Ready-Mix?

For small projects under 1 cubic yard, bags work. For anything over 2-3 yards, ready-mix delivery is almost always cheaper and faster.

40-lb bag: covers 0.30 ft³ -- 90 bags per cubic yard
60-lb bag: covers 0.45 ft³ -- 60 bags per cubic yard
80-lb bag: covers 0.60 ft³ -- 45 bags per cubic yard

A 10x10 patio at 4 inches needs 1.35 yards = 61 eighty-pound bags. Manageable DIY. A 20x30 driveway at 6 inches needs 12.2 yards = 549 bags. Order ready-mix.

Regional Cost Estimates for 2026

Region	Price per yd³	10x10 Patio (1.35 yd³)	20x30 Driveway (12.2 yd³)
Southeast (FL, GA, AL)	$130-$155	$176-$209	$1,586-$1,891
Midwest (OH, IN, IL)	$140-$165	$189-$223	$1,708-$2,013
Southwest (TX, AZ, NM)	$125-$150	$169-$203	$1,525-$1,830
Pacific NW (OR, WA)	$175-$210	$236-$284	$2,135-$2,562
Northeast (NY, NJ, MA)	$190-$230	$257-$311	$2,318-$2,806

Prices include delivery within 15 miles. Fuel surcharges and environmental fees may apply in 2026.

Pro Tips for Accurate Estimation

Use a laser measure for large areas -- tape measures sag over 30+ feet.
Check grade at 4 corners and center -- use a string level or laser level to find high and low spots.
Round up, never down. Suppliers can short-load by 0.25 yards. If you need 2.75, order 3.0.
Call your supplier 2-3 days ahead -- same-day orders cost $50-$100 extra.
Ask about minimum orders. Many suppliers have a 3-4 yard minimum. Below that, a short-load fee of $50-$150 applies.

FAQ

How much extra concrete should I order?

Always order 10% more than your calculated volume. For critical structural work, order 15% extra. The cost of leftover concrete is far less than the cost of a cold joint.

Can I pour concrete in sections to save money?

Yes, but each section requires a construction joint with rebar or keyway. For most residential projects, pouring all at once produces a stronger, more watertight slab.

What if I order too much concrete?

Leftover concrete can be formed into stepping stones, garden borders, or small pads. Never pour excess on the ground -- it is illegal in most jurisdictions.

How do I calculate yardage for circular slabs?

Use: Cubic Yards = (3.14 x radius-squared x depth in feet) / 27. For a 12-ft diameter circle (6 ft radius) at 4 inches: (3.14 x 36 x 0.33) / 27 = 1.38 yd³. Add 10% waste = 1.52 yd³.

Try our free concrete calculator at concreteyardage.com -- instant cubic yards, bag counts, and cost estimates for any project size.