Concrete Calculator
Calculate how much concrete you need for slabs, footings, columns, walls, and stairs. Get cubic yards, number of bags, and cost estimates.
Concrete Calculator
Flat surface like patio, walkway, or floor
Dimensions
Recommended: 5-10% for standard projects
For multiple identical projects (e.g., fence post holes)
Concrete Needed
Bags Needed (Pre-Mixed)
★ 80lb bags are most cost-effective for DIY projects
Ready-Mix Concrete
Order amount (rounded to nearest 0.25 yard)
Estimated Cost
Estimates only. Prices vary by location.
Bags vs Ready-Mix
Bags are best for small projects under 2 cubic yards. For larger projects, ready-mix delivery is more economical and ensures consistent quality.
Standard Depths
Patios: 4 inches. Driveways: 4-6 inches. Footings: 8-12 inches. Posts: 2-3 ft deep. Always check local building codes.
Ordering Tips
Order 10% extra for waste and settling. Have forms fully prepared before delivery. Most ready-mix trucks hold 8-10 cubic yards maximum.
How to Use the Concrete Calculator
Select Your Project Type
Choose the shape that matches your project: slab/square for patios and driveways, footing/column for structural posts, wall for vertical surfaces, or stairs for step calculations.
Enter Your Dimensions
Input the length, width, and depth (thickness) of your project. You can switch between feet/inches and meters. For circular columns, enter the diameter and height instead.
Set Waste Factor
Add a waste percentage (typically 5-10%) to account for spillage, uneven ground, and over-ordering. This ensures you have enough concrete to complete your project without shortages.
Review Your Results
View the calculated volume in cubic yards, number of bags needed (40lb, 60lb, or 80lb sizes), and estimated cost. Use these numbers when ordering ready-mix or buying bags from the store.
Pro tip: Your data is processed entirely in your browser. Nothing is sent to any server, ensuring complete privacy.
Concrete Calculation Guide
Accurately calculating concrete quantities is essential for any construction project. Too little means costly delays and cold joints; too much wastes money and creates disposal challenges. Our calculator helps you get it right the first time.
The basic formula for rectangular concrete projects is simple: Length × Width × Depth. The challenge is converting between measurement systems and accounting for waste, settling, and irregularities in your forms.
Recommended Concrete Depths
- Sidewalks/Patios: 4 inches (standard residential)
- Driveways: 4-6 inches (5+ for heavy vehicles)
- Garage floors: 4-6 inches with thickened edges
- Foundation footings: 8-12 inches (check local codes)
- Post holes: 3× post width, below frost line
Bag Concrete Coverage
- • 40 lb bag: ~0.30 cubic feet
- • 50 lb bag: ~0.375 cubic feet
- • 60 lb bag: ~0.45 cubic feet
- • 80 lb bag: ~0.60 cubic feet
- • 1 cubic yard = ~45 bags (80 lb)
When to Use Ready-Mix
- • Projects over 2 cubic yards
- • Time-sensitive pours
- • Structural applications
- • When consistent PSI is required
- • Access for mixer truck available
Frequently Asked Questions
How do I calculate how much concrete I need?
Calculate concrete volume using Length × Width × Depth for rectangular projects. Our calculator converts dimensions to cubic yards and bags needed. Always add 5-10% extra for waste, settling, and spillage.
How many bags of concrete do I need for a 10x10 slab?
A 10x10 foot slab at 4 inches deep requires about 1.23 cubic yards of concrete. This equals approximately 56 bags of 80lb concrete mix, or 74 bags of 60lb mix. Add 10% extra for waste.
How many 80lb bags of concrete are in a cubic yard?
One cubic yard of concrete requires approximately 45 bags of 80lb concrete mix. Each 80lb bag yields about 0.6 cubic feet when mixed, and there are 27 cubic feet in a cubic yard.
Is it cheaper to mix concrete or buy ready-mix?
For small projects under 2 cubic yards, bags are often cheaper and more practical. For larger projects, ready-mix delivery is more economical ($150-200 per cubic yard) and provides consistent quality with less labor.
How thick should a concrete patio be?
A residential concrete patio should be 4 inches thick. For heavy traffic areas, driveways, or if vehicles will drive on it, use 5-6 inches. Foundation footings typically require 8-12 inches depth.
How much concrete can a truck deliver?
Standard concrete mixer trucks hold 8-10 cubic yards. Mini mixers hold 2-4 cubic yards for smaller projects or limited access areas. Most companies have minimum order requirements (often 1 cubic yard).
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