# Concrete Calculator

Calculate how much concrete you need for your project. Enter slab dimensions to get cubic yards, number of bags (60-lb and 80-lb), and estimated weight.

## What this calculates

Ordering the right amount of concrete is critical for any construction project. Too little means a second pour with an ugly cold joint; too much is wasted money. This calculator takes your slab dimensions (length, width, and depth) and computes the exact volume in cubic feet, cubic yards, and equivalent pre-mixed bags, including an adjustable waste factor.

## Inputs

- **Length** (ft) — min 0
- **Width** (ft) — min 0
- **Depth / Thickness** (in) — min 0 — Standard slab thickness is 4 inches (10 cm)
- **Waste Factor** (%) — min 0, max 50 — Extra concrete for waste and spillage (typically 5-10%)

## Outputs

- **Volume** (ft³)
- **Volume** (yd³) — Order this amount from a concrete supplier
- **Volume (with waste)** (yd³) — Including waste factor
- **60-lb Bags** — Pre-mixed 60-lb bags (0.45 ft³ each)
- **80-lb Bags** — Pre-mixed 80-lb bags (0.60 ft³ each)
- **Estimated Weight** (lbs) — Estimated weight of the concrete pour

## Details

The core formula: Volume = Length × Width × Depth

The depth is entered in inches and automatically converted to feet. Results include:

  - Cubic yards — what you order from a ready-mix supplier (trucks typically carry 8-10 yd³)

  - 60-lb bags — each yields approximately 0.45 ft³ of mixed concrete

  - 80-lb bags — each yields approximately 0.60 ft³ of mixed concrete

Standard concrete depth recommendations:

  - Sidewalks and patios: 4 inches

  - Driveways (cars): 4-6 inches

  - Driveways (heavy vehicles): 6-8 inches

  - Garage floors: 4-6 inches

  - Footings: 8-12 inches or per local code

The waste factor (default 10%) accounts for uneven subgrade, spillage, and over-excavation. For well-prepared sites, 5% is reasonable; for irregular shapes or first-time DIY, consider 10-15%.

## Frequently Asked Questions

**Q: How thick should a concrete slab be?**

A: Standard residential slabs (patios, sidewalks) are 4 inches thick. Driveways should be 4-6 inches for cars and 6-8 inches for trucks. Always check local building codes for specific requirements.

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

A: A 10x10-foot slab at 4 inches deep needs 33.3 ft³ or 1.24 yd³ of concrete. That equals roughly 74 bags of 60-lb mix or 56 bags of 80-lb mix (not including waste).

**Q: Should I use bags or order ready-mix?**

A: For projects under 1 cubic yard, pre-mixed bags are practical. For 1-2 cubic yards, it depends on your labor capacity. For anything over 2 cubic yards, ready-mix delivery is significantly more efficient and cost-effective.

**Q: What is a waste factor and why include it?**

A: The waste factor accounts for concrete lost to spillage, uneven subgrade, and over-excavation. Running short on a pour is far worse than having a little extra. A 10% waste factor is standard practice.

**Q: How much does concrete weigh?**

A: Standard concrete weighs approximately 150 pounds per cubic foot, or about 4,050 pounds (2 tons) per cubic yard. This is important for structural calculations and delivery logistics.

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Source: https://vastcalc.com/calculators/construction/concrete
Category: Construction
Last updated: 2026-04-21