# Cement Calculator

Calculate how many bags of cement you need for your concrete project. Choose your mix ratio and enter dimensions to get accurate cement, sand, and gravel quantities.

## What this calculates

Knowing how many bags of cement to buy before you start mixing saves you a mid-project run to the hardware store. Enter your project dimensions, pick a mix ratio, and this calculator tells you exactly how much cement, sand, and gravel you need.

## Inputs

- **Length** (ft) — min 0
- **Width** (ft) — min 0
- **Depth** (in) — min 0, max 48 — Slabs: 4 in, footings: 8-12 in, walls: 6-8 in
- **Mix Ratio (Cement:Sand:Gravel)** — options: 1:2:3 (Standard), 1:2:4 (Foundation), 1:1.5:3 (Strong), 1:3:6 (Lean) — Standard 1:2:3 mix is good for most residential work
- **Bag Size** — options: 94 lb (1 ft³), 80 lb, 47 lb (half bag)

## Outputs

- **Total Concrete Volume** (ft³)
- **Total Concrete Volume** (yd³)
- **Cement Needed** (ft³)
- **Bags of Cement** (bags) — Rounded up to full bags
- **Sand Needed** (ft³)
- **Gravel Needed** (ft³)

## Details

## Understanding Cement Mix Ratios

A mix ratio like 1:2:3 means 1 part cement, 2 parts sand, and 3 parts gravel by volume. The ratio you choose affects the strength and cost of your concrete.

**Common mix ratios:**
- **1:2:3 (Standard)** -- Good for slabs, driveways, and general construction. Roughly 3,000 PSI.
- **1:1.5:3 (Strong)** -- Higher cement content for structural elements and load-bearing work. About 4,000 PSI.
- **1:2:4 (Foundation)** -- Works well for footings and foundation walls.
- **1:3:6 (Lean)** -- Economy mix for non-structural uses like filling and leveling.

### Why Dry Volume is Higher Than Wet Volume

When you mix dry cement, sand, and gravel with water, the smaller particles fill in the gaps between larger ones. That means you need about 54% more dry material than the final wet concrete volume. This calculator accounts for that automatically.

### Bag Sizes

A standard 94 lb bag of Portland cement equals about 1 cubic foot. If your local store carries 80 lb bags instead, adjust the bag size setting to get the right count.

## Frequently Asked Questions

**Q: How many bags of cement do I need for 1 cubic yard of concrete?**

A: For a standard 1:2:3 mix, you need about 5-6 bags (94 lb each) of Portland cement per cubic yard of concrete. The exact number depends on your mix ratio and how well you compact the dry materials.

**Q: What is the strongest concrete mix ratio?**

A: A 1:1.5:3 ratio produces strong concrete around 4,000 PSI. For even higher strength, a 1:1:2 mix is used in structural engineering, but for most residential work 1:2:3 at roughly 3,000 PSI is more than adequate.

**Q: How much water do I add to a bag of cement?**

A: A general guideline is about 0.5 gallons of water per 94 lb bag of cement when mixed with sand and gravel. The goal is a workable consistency that holds its shape when squeezed but is not soupy. Too much water weakens the finished concrete.

**Q: What is the difference between cement and concrete?**

A: Cement is the powdered binding agent (Portland cement) that makes up about 10-15% of concrete. Concrete is the finished product: cement mixed with sand, gravel, and water. Buying "bags of cement" for site-mixing means you add your own sand and gravel.

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Source: https://vastcalc.com/calculators/construction/cement
Category: Construction
Last updated: 2026-04-08