Concrete Aggregate Calculator: How Much You Need

This concrete aggregate calculator works out the volume and weight of coarse aggregate (gravel or crushed stone) needed for a concrete mix. You enter the slab dimensions (length, width, thickness) and the mix ratio (cement : sand : aggregate), and it returns the aggregate volume in cubic feet or cubic meters and its weight in pounds or kilograms. The calculator uses the standard 1:2:4 mix ratio by volume, which is common for general-purpose concrete, and assumes a typical aggregate density of 150 lb/ft³ (2400 kg/m³).

Formula

The calculator uses the volume method for mix proportioning. The total volume of concrete (wet) is the product of the slab dimensions: V_total = L × W × T, where L and W are in feet, and T is in feet (convert inches to feet by dividing by 12). The volume of aggregate is a fraction of the total volume based on the mix ratio. For a 1:2:4 mix, the sum of parts is 1+2+4=7, so the aggregate fraction is 4/7. The formula is:

V_agg = V_total × (aggregate parts / total parts)

Then the weight is W_agg = V_agg × density, with density typically 150 lb/ft³ for dry loose aggregate (about 2400 kg/m³).

Worked Example

Using the default values: length = 10 ft, width = 10 ft, thickness = 4 in, mix = 1:2:4.

1. Convert thickness to feet: 4 in ÷ 12 = 0.333 ft
2. Total volume: 10 × 10 × 0.333 = 33.3 ft³
3. Aggregate fraction: 4 / (1+2+4) = 4/7 ≈ 0.571
4. Aggregate volume: 33.3 × 0.571 = 19.0 ft³
5. Aggregate weight: 19.0 × 150 = 2850 lb

The calculator shows 19.00 ft³ and 2850 lb, matching the manual calculation.

What Is Concrete Aggregate?

Aggregate is the inert granular material (sand, gravel, crushed stone) that makes up about 60-80% of concrete volume. Coarse aggregate is typically particles larger than 4.75 mm (about 0.19 in), such as gravel or crushed rock. It provides bulk and reduces shrinkage and cost. The most common gradings are 3/4-inch (19 mm) and 1-inch (25 mm) nominal maximum size for general construction. The aggregate quality affects strength: clean, hard, well-graded particles produce stronger concrete.

How to Use the Calculator

Enter the slab or footing dimensions in feet and inches. For a slab, measure the length and width in feet, and the thickness in inches. For a cylindrical column, you would need a different calculator (this one assumes a rectangular prism). Select the mix ratio that matches your project: 1:2:4 (common for footings and slabs), 1:1.5:3 (higher strength for structural beams), or 1:3:6 (lean mix for mass concrete). The calculator assumes you are using a standard Portland cement mix with a water-cement ratio around 0.5, which is typical.

Common Mistakes and Misconceptions

• Mixing up volume and weight: Aggregate is sold by volume (cubic yards) in some places and by weight (tons) in others. The calculator gives both; convert volume to cubic yards by dividing ft³ by 27.
• Ignoring waste: Always order 5-10% extra to account for spillage, uneven subgrades, and compaction.
• Using the wrong density: Loose dry aggregate is about 150 lb/ft³, but wet or compacted aggregate can weigh more. If you buy by weight, use the supplier’s specific gravity.
• Forgetting that the mix ratio is by volume, not weight: A 1:2:4 ratio means one part cement, two parts sand, four parts aggregate by volume. If you use weight batching, you need to adjust for different material densities.

When to Use This Calculator

Use this for small to medium projects like a patio slab, walkway, or footing where you need to order materials. It is not suitable for concrete that requires a specified compressive strength (like structural columns) because that requires a mix design based on weight and water-cement ratio. For those, consult an engineer or use a ready-mix supplier’s calculator.

Alternatives and Adjustments

If you are mixing concrete by hand, you might also need the amount of cement and sand. For a 1:2:4 mix, cement volume = (1/7) × total volume, and sand volume = (2/7) × total volume. Each 94 lb bag of Portland cement is about 1 ft³. So for the example, you’d need about 4.76 ft³ of cement (about 5 bags) and 9.52 ft³ of sand. If you use a different aggregate density (e.g., lightweight aggregate at 100 lb/ft³), adjust the weight accordingly.

Frequently Asked Questions

How many cubic yards of aggregate do I need for a 10×10 slab?

Using the default 4-inch thickness and 1:2:4 mix, the aggregate volume is 19 ft³, which is 19/27 = 0.70 cubic yards. Add 10% waste, so about 0.77 cubic yards.

What is the difference between coarse aggregate and fine aggregate?

Fine aggregate (sand) passes through a 4.75 mm sieve, while coarse aggregate is retained. Both are needed in concrete; the fine fills voids between coarse particles, and the coarse provides bulk and reduces shrinkage.

Can I use this calculator for a circular column?

No, this calculator assumes a rectangular slab. For a cylinder, calculate the volume as πr²h (with r and h in feet), then multiply by the aggregate fraction (4/7 for 1:2:4 mix).

Why does my ready-mix truck deliver less concrete than I calculated?

Concrete shrinks slightly when mixed, and there is always some waste on the ground. Also, the volume of dry materials is not the same as wet concrete; the water causes the mix to compact. Order 5-10% extra to be safe.

What happens if I use too much aggregate?

Too much aggregate makes the mix harsh, hard to place, and may leave voids. The standard ratios are designed to produce workable concrete with adequate cement paste to coat all particles.

How do I convert aggregate weight to tons?

Divide the weight in pounds by 2000 to get short tons. For the example, 2850 lb / 2000 = 1.43 tons. If your supplier uses metric tons, divide by 2204.6.

Related

• Belt Pitch Calculator: Find Your Pulley Spacing
• Bedrock Seed Calculator: Find Your World’s Seed
• Bastion Concrete Calculator: Mix & Volume Guide

in l | Length | ft | 10 | 0
in w | Width | ft | 10 | 0
in t | Thickness | in | 4 | 0
sel ratio | Mix (cement:sand:agg) | 1:2:4=1, 1:1.5:3=1.2, 1:3:6=0.8
out agg_vol | Aggregate volume | ft³ | l*w*(t/12)*(ratio/(1+2+ratio)) | 2
out agg_weight | Aggregate weight | lb | agg_vol*150 | 0