Concrete Calculator
Enter your project dimensions to calculate how much concrete you need. Works for slabs, patios, driveways, footings, and columns.
How Concrete Calculator works
How concrete volume is calculated
For rectangular slabs: Volume = Length × Width × Depth. Convert depth from inches to feet first (divide by 12), then calculate in cubic feet. Divide by 27 to convert to cubic yards (1 cubic yard = 27 cubic feet). For cylindrical columns: Volume = π × radius² × height.
Why add 10% for waste?
Concrete projects typically require 5–15% extra material beyond the calculated volume. Waste comes from: uneven subgrade requiring more depth in places, spillage during pouring, form bulging, and finishing losses. For most residential projects, 10% extra is standard. Complex shapes or sloping ground may need 15–20%.
Bags vs ready-mix delivery
For small projects (under 1 cubic yard), bagged concrete from a hardware store is practical — each 80 lb bag yields about 0.6 cubic feet. For larger projects, ready-mix concrete delivered by truck is more economical and ensures consistent quality. Most ready-mix companies have a minimum order of 1 cubic yard, with short-load fees for orders under their truck capacity.
Common slab thicknesses
Standard residential slab thicknesses: 4 inches for patios, walkways, and garage floors. 6 inches for driveways and areas supporting vehicle traffic. 8–12 inches for foundation footings. Thicker slabs with reinforcing steel (rebar or wire mesh) are needed for heavier loads or poor soil conditions.
Concrete strength and mix ratios
Concrete strength is measured in PSI (pounds per square inch). Common mixes: 2,500 PSI for general residential use, 3,000 PSI for driveways, 3,500–4,000 PSI for commercial and structural applications. The standard mix ratio is 1:2:3 (cement:sand:gravel) by volume. Ready-mix companies specify the strength when you order.
Curing time and weather considerations
Concrete reaches about 70% of its strength within 7 days and full design strength at 28 days. Keep it moist during the first 7 days for proper curing. Do not pour concrete when temperatures are below 40°F (4°C) or above 90°F (32°C) without taking precautions. Rain within 2–4 hours of pouring can damage the surface finish.
Frequently asked questions
How much concrete do I need for a 10×10 slab?
A 10×10 foot slab at 4 inches thick requires 1.23 cubic yards (33.3 cubic feet) of concrete. With 10% waste, order 1.36 cubic yards. This equals about 56 bags of 80 lb concrete mix.
How many bags of concrete per cubic yard?
One cubic yard of concrete requires approximately 45 bags of 80 lb mix or 60 bags of 60 lb mix. For anything over 1 cubic yard, ready-mix truck delivery is usually more practical and economical.
How thick should a concrete patio be?
A standard residential patio should be 4 inches thick. If you plan to drive vehicles across it (e.g., reaching a backyard), increase to 6 inches. Always pour over a compacted gravel base of 4–6 inches for proper drainage and stability.
How much does a yard of concrete cost?
Ready-mix concrete typically costs $125–$175 per cubic yard for material and delivery. Prices vary by region, mix design (strength), and delivery distance. Short-load fees ($15–$50 per yard under the minimum) may apply for small orders. Bagged concrete costs more per yard but has no delivery fee.
Can I pour concrete in the rain?
Do not pour concrete during heavy rain. Light drizzle after the initial set (2–4 hours) is usually acceptable. Rain during pouring dilutes the surface mix, weakening the concrete and causing scaling. If rain is forecast, have plastic sheeting ready to cover the pour immediately.
What is the difference between concrete and cement?
Cement is one ingredient in concrete. Concrete is the finished product made by mixing cement (the binding powder), sand, gravel/aggregate, and water. Portland cement is the most common type. Bagged "concrete mix" contains all four components — just add water.
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