Concrete Calculator

Concrete is the backbone of countless home improvement projects — driveways, patios, sidewalks, deck footings, retaining wall footings, fence post bases, garden borders, and more. Ordering too little concrete is a critical mistake, as a pour must be completed in a single continuous operation; stopping mid-pour creates a cold joint that weakens the structure permanently. Ordering too much wastes money and leaves you with disposal problems. The Concrete Calculator gives you the precise volume needed in both cubic feet and cubic yards, with conversion to standard bag counts for smaller DIY projects.

Ready-mix concrete is measured and ordered in cubic yards. One cubic yard equals 27 cubic feet and weighs approximately 4,050 pounds when cured. Most ready-mix suppliers have a minimum order (typically 1–2 cubic yards) and charge a short-load fee for small orders. For projects under about 0.5 cubic yards, bagged concrete is usually more practical. For anything above 1 cubic yard, ready-mix is significantly more efficient in terms of labour and cost per yard.

A standard 60 lb bag of concrete mix yields approximately 0.45 cubic feet of mixed concrete, and a 80 lb bag yields approximately 0.60 cubic feet. This calculator provides both equivalents so you can choose the bag size available at your hardware store. Note that mixing large quantities of bagged concrete by hand or in a small mixer is physically demanding — budget time accordingly and ensure you have enough water access and proper mixing equipment.

Slab thickness is the single biggest variable in concrete volume calculations. Standard specifications are: 4 inches for residential patios and footpaths; 6 inches for driveways and areas subject to light vehicle traffic; 8 inches for heavier vehicle traffic or weak subsoil conditions. Deck footings and fence post footings are typically 8–12 inches in diameter and extend below the frost line (which varies by geographic location from 0 in tropical climates to 48+ inches in northern states).

Subgrade preparation dramatically affects the actual volume of concrete needed. Soft, yielding, or uneven soil will absorb more concrete than expected. Always compact your subgrade thoroughly and install proper forms before estimating. For large slabs, minor undulations in the subgrade can add 5–15% to actual consumption, which is why a 10% overage is the industry standard minimum. Increase overage to 15–20% for rough or uncertain subgrades.

Before ordering ready-mix, confirm your access route, the truck clearance (a fully loaded mixer truck typically needs 12 feet of horizontal clearance and 14 feet of vertical clearance), and how far the truck can reach with the chute (typically 10–18 feet). For locations inaccessible to the truck, a concrete pump truck can be rented, but this adds significant cost. Alternatively, a power buggy or wheelbarrows can move concrete from the chute to the pour area.

Temperature matters greatly for concrete curing. The ideal temperature range for pouring and curing is 50–90°F (10–32°C). Below 40°F (4°C), hydration slows dramatically and the mix can freeze if not protected, leading to a structurally unsound result. Above 90°F (32°C), concrete sets too quickly, making it difficult to finish properly. Schedule your pour accordingly and have a curing plan ready — burlap, plastic sheeting, or curing compound to retain moisture during the 28-day curing period.