How Many Bags of Concrete Do I Need? 40, 60 & 80 lb Guide
Learn how to calculate the exact number of retail concrete bags (40 lb, 50 lb, 60 lb, and 80 lb) required for any slab, post hole, or footing—with product-specific yield data and ordering rules.
Total Bags = Total Cubic Feet Required ÷ Product Yield per Bag
Calculate your slab's cubic volume in feet, multiply by 1.10 (10% waste buffer), divide by the bag's cubic-foot yield, and round up to the next full whole bag.
Interactive Bag Calculator Tool
Concrete Volume & Coverage Calculator
Convert dimensions, cubic yards, and bags into precise surface coverage and order quantities.
Comparing bagged mix against a ready-mix truck?
Use our Concrete Slab Calculator to compare ready-mix delivery rates with bagged costs and delivery fees.
The 4-Step Process for Sizing Concrete Bags
Because concrete bags are packaged by dry weight (pounds) while excavations require three-dimensional volume (cubic feet), you must follow a structured conversion process:
- Determine Total Excavation Volume:
Multiply Length in feet × Width in feet × Thickness in feet (Thickness in inches ÷ 12).
Example: An 8 ft × 10 ft patio at 4 inches thick = 8 × 10 × (4 ÷ 12) = 26.67 cubic feet. - Factor In a Waste & Subgrade Allowance:
Multiply the nominal cubic feet by 1.10 (10% buffer) to account for uneven dirt, spillage, and form deflection.
Example: 26.67 cu. ft. × 1.10 = 29.33 cubic feet total required. - Divide by the Bag's Stated Yield:
Divide total required volume by the published cubic-foot yield of your selected bag size.
For 80 lb bags: 29.33 ÷ 0.60 = 48.88 bags.
For 60 lb bags: 29.33 ÷ 0.45 = 65.18 bags. - Round Up to Whole Bags:
Because home improvement stores sell bags in whole units only, always round upward to the next integer.
Purchase: 49 bags (80 lb) or 66 bags (60 lb).
Concrete Bag Size Yield & Coverage Comparison Table
This table compares yields, coverage at 4 inches depth, dry weight, and bags needed per cubic yard for all four standard North American dry pre-mix bag sizes:
| Bag Size | Typical Yield (ft³) | Coverage @ 4" Slab | Bags per Cubic Yard | Dry Weight per Yard | Best Application |
|---|---|---|---|---|---|
| 80 lb (36.3 kg) | 0.60 cu. ft. | 1.80 sq. ft. | 45 bags | 3,600 lbs (1.8 tons) | Most economical for patios, walkways & large pours |
| 60 lb (27.2 kg) | 0.45 cu. ft. | 1.35 sq. ft. | 60 bags | 3,600 lbs (1.8 tons) | Easier solo lifting; small pads, steps & fence posts |
| 50 lb (22.7 kg) | 0.375 cu. ft. | 1.13 sq. ft. | 72 bags | 3,600 lbs (1.8 tons) | Fast-setting post mix & mailbox footing setting |
| 40 lb (18.1 kg) | 0.30 cu. ft. | 0.90 sq. ft. | 90 bags | 3,600 lbs (1.8 tons) | Lightweight carry for repairs, caps & tight access |
* Yield assumptions reflect standard high-strength general-purpose concrete mixes. For depth-by-depth coverage tables on 80-lb bags, see our 80 lb bag coverage guide or our 80 lb bags in a yard conversion reference.
Bags Needed for Slabs, Sidewalks, Patios & Post Holes
This reference chart displays exact bag requirements (including a 10% safety allowance) across common DIY residential concrete projects:
| Project Type & Size | Thickness | Volume (+10% Waste) | 80 lb Bags Needed | 60 lb Bags Needed |
|---|---|---|---|---|
| 6 × 6 ft Small Shed Pad | 4 inches | 13.20 cu. ft. (0.49 yd³) | 22 bags | 30 bags |
| 8 × 8 ft Small Patio | 4 inches | 23.47 cu. ft. (0.87 yd³) | 40 bags | 53 bags |
| 10 × 10 ft Standard Patio | 4 inches | 36.67 cu. ft. (1.36 yd³) | 62 bags | 82 bags |
| 12 × 12 ft Outdoor Living Pad | 4 inches | 52.80 cu. ft. (1.96 yd³) | 88 bags | 118 bags |
| 3 × 20 ft Garden Walkway | 4 inches | 22.00 cu. ft. (0.81 yd³) | 37 bags | 49 bags |
| Fence Post (8" dia × 36" deep, 4x4 post) | 36" deep | 0.78 cu. ft. net | 2 bags | 2 bags (or 2-3 of 50 lb) |
| Deck Pier (12" Sonotube × 48" deep) | 48" deep | 3.14 cu. ft. | 6 bags | 7 bags |
Bags vs. Ready-Mix Truck: Where Is the Breakeven Point?
Before loading dozens of heavy bags into your truck bed, evaluate the total project volume and physical mixing limits:
When to Buy Bagged Concrete:
- Volume Under 1.0 Cubic Yard (< 40–45 bags): Fence posts, deck footings, stepping stones, small mower pads, and equipment bases.
- Tight or Inaccessible Backyards: Sites where a 30-ton ready-mix truck cannot access the pour area and concrete pumping is cost-prohibitive.
- Phased / Multi-Day Work: Projects poured in independent sections over multiple weekends.
When to Order a Ready-Mix Truck:
- Volume Exceeding 1.0–1.5 Cubic Yards (> 45–65 bags): Patios, driveways, garage floors, large walkways, and structural slabs.
- Uniform Strength & Finish: Mixing 60+ bags in a portable drum mixer takes 3 to 4 hours, creating uneven hydration curing and cold joints.
- Labor & Delivery Value: A ready-mix truck discharges 5 yards in 15 minutes, saving dozens of hours of strenuous labor.
For comprehensive ready-mix price ranges and short-load fees, check our 2026 concrete cost per yard guide and our guide on how to calculate concrete yardage.
Frequently Asked Questions About Concrete Bags
How many bags of concrete do I need for a 10x10 slab?
For a 10×10 foot slab poured at 4 inches thick (33.33 cu. ft. nominal volume), you will need 62 bags of 80 lb concrete (or 82 bags of 60 lb concrete), factoring in a standard 10% safety allowance (36.67 cu. ft. total). Without waste, the exact mathematical requirement is 56 bags (80 lb) or 75 bags (60 lb).
How many 80 lb bags of concrete make a cubic yard?
Under the standard yield assumption of 0.60 cubic feet per 80-pound bag, it takes 45 bags to equal one full cubic yard (27 cu. ft. ÷ 0.60 = 45 bags). Always verify the stated yield on your product packaging, as specialty formulations may vary.
How many 60 lb bags of concrete make a cubic yard?
A standard 60-pound bag yields approximately 0.45 cubic feet of mixed concrete. It takes 60 bags of 60-lb concrete to equal one cubic yard (27 cu. ft. ÷ 0.45 = 60 bags).
When is it cheaper to order a ready-mix truck instead of bags?
The financial and physical breakeven point is typically around 1.0 to 1.5 cubic yards (45 to 70 eighty-pound bags). While bags are cheaper for small jobs under 35 bags (~0.75 cu. yds), hand-mixing more than 40 bags is physically exhausting, risks inconsistent curing, and ready-mix trucks become more cost-effective despite small-load fees.
Do fast-setting or high-strength concrete bags yield the same volume?
Standard high-strength concrete mixes (such as QUIKRETE® Concrete Mix #1101 or Sakrete® High Strength) typically yield 0.60 cu. ft. per 80 lb and 0.45 cu. ft. per 60 lb. However, specialized lightweight mixes (e.g. QUIKRETE Q•MAX PRO) or fast-setting post mixes may have different densities and yields. Always check the technical data sheet on the bag.