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How Many Bags of Concrete Do I Need? Calculator + Chart
Enter your area and thickness — get the exact number of 40, 60, and 80 lb bags you need from Quikrete or Sakrete, plus cost estimate and the point where ready-mix beats bags on price.
Free Tool
Bags of Concrete Calculator
Enter area in square feet and thickness in inches. Results show all bag sizes plus cost and break-even point.
Results include 10% overage. Bag yields: 40 lb = 0.30 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³, Fast-Set 50 lb = 0.375 ft³ (Quikrete/Sakrete specs).
Quick Reference
Bags of Concrete Needed — By Area & Thickness
All figures include 10% overage. Based on 80 lb bag yield of 0.60 ft³ (Quikrete/Sakrete specification).
| Area (sq ft) | 3.5" thick | 4" thick | 6" thick | 8" thick | Notes |
|---|---|---|---|---|---|
| 10 sq ft | 6 | 7 | 10 | 14 | Post hole, small patch |
| 25 sq ft | 14 | 16 | 24 | 32 | Small step or landing |
| 50 sq ft | 27 | 31 | 46 | 62 | Small patio section |
| 100 sq ft (10×10) | 54 | 62 | 93 | 124 | Small patio / shed floor |
| 200 sq ft | 108 | 124 | 185 | 247 | Single-car driveway section |
| 400 sq ft (20×20) | 216 | 247 | 370 | 494 | Large patio / 2-car drive |
| 576 sq ft (24×24) | 311 | 356 | 533 | 711 | 2-car garage floor |
| 1,000 sq ft | 540 | 617 | 926 | 1,234 | Use ready-mix — bags uneconomical |
All figures are 80 lb bags with 10% overage. Divide by 1.33 for 60 lb bags, multiply by 2 for 40 lb bags. For projects over 200 sq ft at 4"+, ready-mix is almost always cheaper — see comparison below.
Definitive Reference
How Many Bags Per Cubic Yard — All Sizes
| Bag Size | Yield per bag | Bags per yd³ | Price range | Cost per yd³ | Best for |
|---|---|---|---|---|---|
| 40 lb | 0.30 ft³ | 90 | $5–$7 | $450–$630 | Patches, small repairs |
| 50 lb Fast-Set | 0.375 ft³ | 72 | $7–$9 | $504–$648 | Post holes, deck footings |
| 60 lb | 0.45 ft³ | 60 | $7–$10 | $420–$600 | Footings, smaller slabs |
| 80 lb | 0.60 ft³ | 45 | $9–$13 | $405–$585 | Most DIY projects — best value |
| Ready-mix | — | — | $120–$165/yd³ | $120–$165 | Any project over 1 yd³ |
Common Project Examples — How Many Bags
| Project | Dimensions | Yd³ | 80 lb bags | Use ready-mix? |
|---|---|---|---|---|
| Post hole (4×4) | 10" dia × 36" deep | 0.06 | 2–3 | No — use bags |
| Post hole (6×6) | 12" dia × 42" deep | 0.10 | 3–4 | No — use bags |
| Small patio (10×10) | 100 sq ft × 4" | 1.37 | 62 | Borderline — truck min charge may apply |
| Standard patio (20×20) | 400 sq ft × 4" | 5.5 | 247 | Yes — ready-mix saves ~$2,000 |
| Single-car driveway | 40×12 ft × 6" | 9.8 | 441 | Yes — ready-mix saves ~$3,500 |
| Garage floor (24×24) | 576 sq ft × 4" | 7.9 | 356 | Yes — ready-mix saves ~$2,800 |
Common Questions
Bags of Concrete FAQ
A 10×10 ft slab at 4 inches thick requires about 1.37 cubic yards with 10% overage. At 45 bags per cubic yard, you need approximately 62 bags of 80 lb concrete. At 4 inches, this project is borderline for ready-mix — call your local plant to check the minimum order charge. If they charge a $300+ minimum, 62 bags at $11 each ($682) may actually cost less than the ready-mix minimum.
For a standard 4×4 deck post in a 10-inch diameter hole at 36 inches deep, you need 2 bags of 80 lb Quikrete (or 3 bags of 50 lb Fast-Set). For a 6×6 post in a 12-inch hole at 42 inches deep, use 3–4 bags of 80 lb. Quikrete Fast-Set is the best choice for post holes — it reaches working strength in 4 hours and can be dry-poured directly into the hole without mixing.
80 lb bags are the better value for most DIY projects — lower cost per cubic foot than 60 lb bags and fewer trips to mix. The exception: if you're mixing by hand and the 80 lb weight is difficult to manage, 60 lb bags are ergonomically easier. Both produce the same strength concrete. 40 lb bags are only cost-effective for small patches where you need very little material.
One cubic yard = 27 cubic feet. Bag yields: 80 lb bag = 0.60 ft³ (45 bags/yd³), 60 lb bag = 0.45 ft³ (60 bags/yd³), 40 lb bag = 0.30 ft³ (90 bags/yd³). These are Quikrete and Sakrete published specifications. Always add 10% extra to account for waste.
The break-even is approximately 1 cubic yard. Above 1 yard, ready-mix is almost always cheaper: 45 bags of 80 lb at $11 each = $495 vs $125–$165 for ready-mix delivery. For a 20×20 patio (5.5 yd³), bags cost ~$2,700 in material alone vs ~$690 for ready-mix — a saving of $2,000 on material before you account for your mixing time.
Bag yield figures verified against Quikrete and Sakrete published product data sheets. Break-even calculations based on NRMCA 2026 regional pricing and Home Depot/Lowe's bag price surveys in 8 US markets. Updated June 2026.