Calculate how much concrete you need for slabs, footings, and columns. Get results in cubic yards, cubic feet, and number of bags.
Auto-updated · Verified daily against IRS, Fed & Treasury sources
Enter your numbers below
A DIY homeowner in Ohio is building a 16×20 ft pressure-treated pine deck. Wants to calculate board footage, joist spacing requirements, and total material cost before going to the lumber yard.
Takeaway: Lumber prices fluctuate 30-50% based on housing market cycles — 2026 prices are down from 2021 peaks. Add 10% waste factor to board counts for cuts and defects. Composite decking (Trex, etc.) costs 2-3× more but eliminates annual staining.
Lumber calculations typically add 10-15% for cuts and defects. Tile installations in rooms with obstacles (cabinets, islands) need 15-20% extra. Straight-line flooring installations need 5-10%. Applying a flat waste factor to all project types leads to significant under- or over-ordering.
Calculators for beam sizing, deck load, and structural spans provide estimates only. Actual structural work (load-bearing wall removal, deck ledger attachment, header sizing) requires permits and often a licensed engineer's stamp. Using undersized members based on a web calculator without engineer review creates safety and liability risk.
Wire gauge calculators for circuit sizing assume straight runs. Every 90-degree bend, junction box, and conduit fill fraction introduces derating factors. The NEC (National Electrical Code) derate rules for conductors in conduit, ambient temperature, and bundled cables can require upsizing by 1-2 wire gauges beyond the basic ampacity calculation.
Joist span tables, snow load requirements, and stud spacing rules vary by jurisdiction. A 2×10 joist spanning 14 feet may pass in a low-snow-load area and fail in a high-alpine zone. Always cross-reference with your local building department's adopted code edition (IBC, IRC) before finalizing material specifications.
Based on your inputs
yd³ (with waste)
| Cubic Feet (no waste) | 33.33 ft³ |
|---|---|
| Cubic Yards (with waste) | 1.36 yd³ |
| Cubic Meters | 0.944 m³ |
| 60-lb Bags Needed | 62 bags |
| Estimated Weight | 5500 lbs |
Quick tip: For less than 1 yd³, use bags. For 1+ yd³, order ready-mix concrete.
Analyze 3+ calcs to unlock your Financial Picture dashboard (cross-analysis of all your numbers).
Calculating how much concrete you need prevents two costly mistakes: ordering too little (causing cold joints and delays) or too much (wasting money). This guide covers concrete volume calculations for slabs, footings, and columns with practical examples.
Rectangular slab or footing: Volume (cu ft) = Length (ft) x Width (ft) x Depth (inches) / 12
Cylindrical column or pier: Volume (cu ft) = pi x (Diameter/2)^2 x Height, with diameter in feet
Convert to cubic yards: Divide cubic feet by 27
A 20 x 20 foot patio at 4 inches thick:
Volume = 20 x 20 x (4/12) = 133.3 cu ft
Cubic yards = 133.3 / 27 = 4.94 cu yd
With 10% waste = 5.43 cu yd
Order: 5.5 cubic yards of ready-mix
If mixing your own concrete (recommended for under 1 cubic yard only):
40-lb bags: 56 bags per cubic yard
60-lb bags: 45 bags per cubic yard
80-lb bags: 37 bags per cubic yard
For our 5.5 cu yd patio example, you would need 204 sixty-pound bags -- at that quantity, ready-mix delivery is far more practical and usually cheaper.
Sidewalks and patios (foot traffic): 4 inches
Driveways (passenger cars): 5-6 inches
Garage floors: 4-6 inches with wire mesh
Heavy vehicle areas: 6-8 inches with rebar
Foundations and footings: 8-12 inches minimum, per local code
Standard residential footings are typically twice the wall width and at least 8 inches deep. A 40-foot perimeter footing at 16 inches wide and 8 inches deep = 40 x 1.33 x 0.67 = 35.6 cu ft = 1.32 cu yd. Use our gravel calculator for the drainage base beneath your footing.
Ready-mix trucks typically deliver in increments of 0.25 to 0.5 cubic yards. Minimum orders are usually 1 cubic yard, with short-load fees for orders under the truck minimum (typically 8-10 cu yd). Always round up your order -- extra concrete costs far less than a second delivery.
A concrete driveway is one of the most durable home improvements, lasting 25-50 years with proper installation. This guide helps you calculate the concrete volume, estimate costs, and understand the specifications for a driveway that will stand up to daily vehicle traffic.
Minimum thickness: 4 inches (residential, light vehicles only)
Recommended thickness: 5-6 inches (standard residential with SUVs/trucks)
Heavy-duty: 6-8 inches (RVs, heavy trucks, commercial)
Concrete strength: Minimum 3,500 PSI for driveways. 4,000 PSI recommended for cold climates. Air-entrained concrete is essential in freeze-thaw regions.
Standard two-car driveway: 20 ft wide x 40 ft long x 5 inches thick
Volume = 20 x 40 x (5/12) = 333 cu ft = 12.35 cu yd
With 10% waste = 13.6 cu yd
Order: 14 cubic yards of ready-mix
Concrete only: $130-$175 per cubic yard delivered
Total installed cost: $8-$18 per square foot
For a 20 x 40 ft driveway: $6,400-$14,400 total
This includes grading, forms, gravel base, concrete, finishing, and curing.
A proper driveway needs a compacted gravel base of 4-8 inches. Use our gravel calculator to estimate the base material. The subgrade must be compacted to 95% density. Poor base preparation is the number one cause of driveway cracking and settling.
Wire mesh (6x6 W1.4/W1.4): Standard for 4-inch slabs, $0.15-$0.25/sq ft
Rebar (#3 or #4, 18" grid): Better for 5-6 inch slabs, $0.40-$0.70/sq ft
Fiber mesh: Added to the concrete mix, $0.10-$0.20/sq ft, reduces surface cracking
Control joints should be cut every 8-12 feet to control where cracking occurs. The rule of thumb is joint spacing in feet should not exceed 2-3 times the slab thickness in inches.
The decision between mixing your own concrete from bags and ordering ready-mix delivery depends on project size, accessibility, and budget. This guide helps you determine the break-even point and understand the trade-offs for each option.
Bagged concrete makes sense for small projects under 0.5 cubic yards (about 13.5 cubic feet). Common uses include:
- Fence post holes (1-2 bags each)
- Small repair patches
- Mailbox posts
- Setting deck post anchors
- Small pads under 15 sq ft at 4 inches thick
40-lb bag: 0.011 cu yd (0.30 cu ft) -- sets a 4" post hole
50-lb bag: 0.0139 cu yd (0.375 cu ft)
60-lb bag: 0.017 cu yd (0.45 cu ft)
80-lb bag: 0.022 cu yd (0.60 cu ft) -- most cost-effective per unit
Cost per bag: $4-$7 at home improvement stores. At $5.50 per 80-lb bag, one cubic yard of bagged concrete costs approximately $204 -- comparable to delivered ready-mix but with significant labor added.
For projects over 1 cubic yard, ready-mix delivery is almost always the better choice:
- Consistent mix quality (professionally batched)
- Much faster placement (a truck pours 10 cu yd in 30 minutes vs. hours of mixing)
- Less physical labor
- Cost-competitive at $130-$175 per cubic yard delivered
Ready-mix becomes cheaper than bags at approximately 0.75 to 1.0 cubic yard, when you factor in your time. At 1 cu yd, you would mix 37 eighty-pound bags by hand -- about 3-4 hours of hard labor. A truck delivers and pours that in minutes.
For 1-3 cubic yard projects, consider:
Short-load trucks: Ready-mix with a small-load fee ($50-$100 extra). Still easier than bags.
Trailer mix services: Some suppliers rent concrete mixing trailers that you tow to your site. Typically 1 cu yd capacity.
Use our concrete calculator to determine your exact volume, then decide which option fits your project. For the supporting gravel base, check our gravel calculator.
Volume (cu ft) = length × width × thickness. Convert to cubic yards by dividing by 27. Add 10% waste.
60-lb bags: 45 bags per cu yd. 80-lb bags: 37 bags per cu yd. 40-lb bags: 56 bags per cu yd.
Foot traffic only: 4 inches. Driveways/light vehicles: 6 inches. Heavy loads: 8+ inches.
1 cubic yard of concrete weighs approximately 4,050 lbs (1,837 kg).
Use the formula Volume equals pi times radius squared times height, with all measurements in feet. Divide the result by 27 to convert cubic feet to cubic yards and add 10 percent for waste.
Cement is one ingredient in concrete, acting as the binding agent. Concrete is the finished product made by mixing cement with sand, gravel, and water in specific proportions for structural strength.
Calculate each step as a small rectangular volume by multiplying width times depth times rise height. Sum all steps together, convert to cubic yards by dividing by 27, and add 10 to 15 percent for waste.
Concrete reaches about 70 percent of its rated strength after 7 days and full design strength at 28 days. Keep it moist during the first week to prevent cracking and ensure maximum durability.
Calculate the footing volume as length times width times depth in feet, then divide by 27 for cubic yards. Rebar does not significantly reduce the concrete volume needed, so no deduction is necessary.
Slab: V = L × W × (D/12) (ft³)
Cu Yards = V ÷ 27 × (1 + waste%)
Bags: 60-lb = 45 bags/cu yd
Every formula on this page traces to a federal agency, central bank, or peer-reviewed institution. We cite the rule-makers, not secondhand blogs.
Found an error in a formula or source? Report it →
Calculations are for educational purposes only. Consult a qualified financial advisor for personalized advice.