Concrete guide
How Much Concrete Do I Need for a 10x10 Slab?
(Length × Width × Depth ÷ 12) ÷ 27 = Cubic Yards. Pouring more than 2 cu yds? Skip the bags and order a ready-mix truck.
Why 4 Inches Is the Magic Number
Slab thickness changes your concrete order more than any other input:
| Project | Thickness | 10x10 Concrete Needed |
|---|---|---|
| Patio / walkway / shed base | 4 in | 1.23 cu yds (56 bags) |
| Driveway / vehicle parking | 5-6 in | 1.54-1.85 cu yds (70-84 bags) |
| Heavy RV / truck pad | 6 in+ | 1.85+ cu yds (84+ bags) |
Thickness multiplies volume directly: going from 4in to 6in on a 10x10 uses 50% more concrete (1.85 vs 1.23 cu yds). Decide thickness before you order, not at the store.
The Step-by-Step Formula
Step 1: Measure Your Slab
| Measurement | Example | Notes |
|---|---|---|
| Length | 10 ft | Longest side of the pour |
| Width | 10 ft | For L-shapes, split into rectangles and add |
| Depth | 4 in | Patios/walkways; use 5-6in for driveways |
Step 2: Apply the Formula
Base Volume (cubic feet) = Length × Width × (Depth ÷ 12) = 10 × 10 × (4 ÷ 12) = 33.3 cu ft Cubic Yards = Base Volume ÷ 27 = 33.3 ÷ 27 = 1.23 cu yds
Step 3: Convert to Bags
80lb bag yield = 0.60 cu ft (NRMCA guidance) Bags Needed = Base Volume ÷ 0.60 = 33.3 ÷ 0.60 = 56 bags With 10% Waste Margin = 56 × 1.10 = 62 bags
Other bag sizes scale by weight: a 60lb bag yields 0.45 cu ft, a 40lb bag 0.30 cu ft.
Step 4: Decide Bags vs Truck
- ≤ 1 cu yd (~45 bags of 80lb): bagged mix is practical DIY
- > 2 cu yds: order a ready-mix truck — cheaper per yard, no mixing labor
- 1-2 cu yds: judgment call — your back will have an opinion
Coverage Shortcut
1 cubic yard at 4 inches covers 81 square feet. With a 10% waste margin, plan on 73-75 sq ft per yard. Quick check: 100 sq ft slab ÷ 81 = 1.23 cu yds — same answer as the long formula.
Worked Example: 24ft × 12ft Patio at 4in
| Parameter | Value |
|---|---|
| Dimensions | 24ft × 12ft × 4in |
| Base Volume | 24 × 12 × (4÷12) = 96 cu ft |
| Cubic Yards | 96 ÷ 27 = 3.56 cu yds |
| With 10% Waste | 3.56 × 1.10 = 3.91 cu yds |
| Bag Equivalent | 96 ÷ 0.60 = 160 bags → 176 with waste |
Order: a 4.0 cu yd ready-mix truck. At 3.91 cu yds this is well past the bags-vs-truck breakeven — 176 bags would mean roughly 3 hours of continuous mixing.
5 Common Mistakes to Avoid
1. Skipping the 10% Waste Margin
Mistake: Buying exactly 56 bags for a 10x10
Result: Subgrade is never perfectly level — low spots eat 5-10% extra volume and you run short mid-pour
Fix: Always order ×1.10 (62 bags for a 10x10)
2. Mixing Units
Mistake: Feet × inches ÷ 27
Result: Order 12x too much or too little
Fix: Convert depth to feet first: inches ÷ 12
3. Pouring 4in Where 6in Is Needed
Mistake: Using patio thickness for a driveway
Result: Cracking under vehicle loads within the first year
Fix: 4in for foot traffic, 5-6in for vehicles
4. Assuming All Bags Yield the Same
Mistake: Calculating with 80lb yield but buying 60lb bags
Result: 25% short — 60lb bags yield 0.45 cu ft, not 0.60
Fix: Match the yield to the bag: 80lb = 0.60, 60lb = 0.45, 40lb = 0.30 cu ft
5. Ignoring the Subgrade
Mistake: Calculating from nominal dimensions only
Result: Soft or uneven ground adds hidden depth and eats your margin
Fix: Compact and level the base before finalizing your order
When to Call a Professional
DIY is fine for:
- Pours under 1 cu yd
- Simple rectangular patios and walkways
- Ground-level slabs with good drainage
Call a pro when:
- Pour exceeds 2 cu yds (truck scheduling + finishing crew)
- Structural or load-bearing slabs
- Slopes, steps, or drainage problems on site
- Freeze-thaw climates requiring footings below frost line
Next Steps
- Calculate your slab: Use BuildCalc's Concrete Calculator — volume, bags, and waste margin in one step
- Price both options: Bag total vs truck minimum (most suppliers have a short-load fee under 4-5 yds)
- Prep before delivery: Forms set, base compacted, reinforcement placed
- Plan the finish: Concrete waits for no one — line up help for screeding and floating
Free Tool: BuildCalc Concrete Calculator — no login, instant results, bag counts for 40/60/80lb included.
FAQ
How much concrete do I need for a 10x10 slab?
At 4-inch thickness: 1.23 cubic yards — 56 bags of 80lb mix, order 62 with a 10% waste margin. At 6-inch thickness: 1.85 cubic yards (84 bags, order 92).
How many 80lb bags of concrete make a cubic yard?
45 bags. One 80lb bag yields 0.60 cubic feet (NRMCA guidance), and one cubic yard is 27 cubic feet: 27 ÷ 0.60 = 45.
Should I buy bagged concrete or order a ready-mix truck?
Up to 1 cubic yard (~45 bags of 80lb), bagged mix is practical DIY. Over 2 cubic yards, a ready-mix truck is cheaper per yard and saves hours of mixing. Between 1 and 2 yards is a judgment call.
How many square feet does a cubic yard of concrete cover?
At 4-inch thickness, 1 cubic yard covers 81 square feet. With a 10% waste margin, plan on 73-75 sq ft per yard.
What thickness should my slab be?
4 inches for patios, walkways, and shed bases; 5-6 inches for driveways and vehicle parking. A 10x10 at 6 inches uses 50% more concrete than at 4 inches.
References
- NRMCA — National Ready Mixed Concrete Association (bagged mix yield guidance: 0.60 cu ft per 80lb bag)
- ASTM C94 — Standard Specification for Ready-Mixed Concrete
- ACI 318 — American Concrete Institute structural concrete code (residential flatwork thickness guidance)