Question 1

How many bags of concrete do I need for a 10x10 slab?

Accepted Answer

For a 10×10 foot slab at the standard 4-inch depth, you need about 1.23 cubic yards or approximately 15 bags of 80lb concrete mix. At 6 inches deep (typical for driveways), you need about 1.85 cubic yards or 23 bags. Always add 10% extra for spillage and uneven ground.

Question 2

How thick should a concrete slab be?

Accepted Answer

Standard residential slabs (patios, walkways) are 4 inches thick. Driveways and garage floors need 6 inches minimum. Foundations and footings typically require 8-12 inches depending on local building codes and soil conditions. Always consult local codes for structural requirements.

Question 3

What is the difference between a cubic yard and a cubic foot of concrete?

Accepted Answer

One cubic yard equals 27 cubic feet. Ready-mix concrete trucks deliver in cubic yards — a standard truck carries 8-10 cubic yards. For small projects under 1 cubic yard, pre-mixed bags (60lb or 80lb) are more practical and cost-effective than ordering a truck delivery.

Question 4

How many 80lb bags of concrete make a cubic yard?

Accepted Answer

You need approximately 45 bags of 80lb concrete mix to make one cubic yard. Each 80lb bag yields about 0.6 cubic feet of mixed concrete. For large projects (over 2-3 cubic yards), ready-mix delivery is more economical and provides better consistency than mixing individual bags.

Question 5

Should I order extra concrete beyond the calculated amount?

Accepted Answer

Yes — order 10% more concrete than calculated. This accounts for spillage, uneven subgrade, slight measurement errors, and the concrete that sticks to mixing equipment. For delivered ready-mix, rounding up to the nearest half or full yard is standard practice.

Question 6

When should I use ready-mix vs bagged concrete?

Accepted Answer

Use bagged concrete (60lb or 80lb bags) for small projects under 1-2 cubic yards — fence posts, small slabs, and repair work. For projects over 2 cubic yards, ready-mix concrete delivery is faster, cheaper per yard, and provides more consistent quality. The break-even point is typically around 1.5-2 cubic yards.

Question 7

How long does concrete take to cure?

Accepted Answer

Concrete reaches about 70% of its full strength in 7 days and achieves its rated strength (typically 4,000 PSI) in 28 days. You can walk on it after 24-48 hours and drive on it after 7 days. Keep it moist during the first week by misting or covering with plastic sheeting for optimal curing.

Concrete Calculator — How Much Concrete Do I Need?