Gravel Calculator

Weight (short tons) = volume (yd³) × bulk density (lb/ft³) ÷ 2,000

L

Length of the area, in feet

W

Width of the area, in feet

D

Depth of the gravel layer, in inches

ρ

Bulk density of the stone, in kilograms per cubic metre

Use it for a driveway, a path, a drainage trench, a shed base or a french drain — anywhere a layer of loose stone is spread over a rectangle. Compaction is the number to watch: the tonnage here is loose stone at its bulk density, and a layer rolled to refusal takes another 10% to 20%.

1. A 20 ft by 10 ft driveway, three inches of crushed stone

   1. Area: 20 × 10 = 200 square feet
   2. Depth in feet: 3 ÷ 12 = 0.25 ft
   3. Volume: 200 × 0.25 = 50 cubic feet = 50 ÷ 27 = 1.85 cubic yards
   4. Crushed stone is about 100 lb per cubic foot, so 50 × 100 = 5,000 lb
   5. 5,000 ÷ 2,000 = 2.50 short tons, which is 2.27 tonnes

   Order 2.5 tons and expect the yard to load slightly over — a loader bucket is not a scale. If the supplier sells by the yard instead, 1.85 cubic yards is the number to ask for.

2. A 30 ft by 10 ft drainage run, four inches of river rock

   1. Area: 30 × 10 = 300 square feet
   2. Depth in feet: 4 ÷ 12 = 0.333 ft
   3. Volume: 300 × 0.333 = 100 cubic feet = 3.70 cubic yards
   4. River rock runs about 94 lb per cubic foot: 100 × 94 = 9,400 lb
   5. 9,400 ÷ 2,000 = 4.68 short tons, which is 4.25 tonnes

   River rock is the lightest of the three stones here, so the same volume weighs about 6% less than crushed stone — which is the entire reason the density is a column in the table below rather than a constant in the formula.

The densities are typical figures for loose, dry stone: about 100 lb per cubic foot for crushed stone, 96 for pea gravel and 94 for river rock. A real load varies with the quarry, the gradation and above all with moisture and how much the stone has settled in the truck — a wet, compacted load can be 10% heavier than a dry one. Depth means the finished, compacted depth; stone spread three inches loose will settle below three. The area is treated as a rectangle, and a curved or tapering bed takes less than the full rectangle suggests.

How many tons of gravel do I need?

Work out the volume in cubic yards, then multiply by the weight of one cubic yard of that stone. Crushed stone is about 1.35 short tons per cubic yard, pea gravel about 1.30 and river rock about 1.26, so the driveway above (1.85 cubic yards) takes about 2.5 short tons. In metric the same figures are 1.6, 1.54 and 1.5 tonnes per cubic metre.

How much does a cubic yard of gravel weigh?

Between 1.26 and 1.35 short tons depending on the stone — crushed stone is the heaviest of the three and river rock the lightest. In metric the same cubic yard of crushed stone is 1,223 kilograms, or 1.22 tonnes, because a cubic yard is only 0.765 of a cubic metre; it is a full cubic metre of the same stone that weighs 1.6 tonnes.

What is the difference between a short ton and a tonne?

A short ton is 2,000 pounds; a tonne is 1,000 kilograms, which is 2,204.6 pounds. So a tonne is about 10% heavier, and the same pile of crushed stone is either 2.50 short tons or 2.27 tonnes. Quoting the wrong one is a 10% error on the invoice, which is why both rows are on the calculator.

How deep should a gravel driveway be?

Four inches of crushed stone is the usual surface over firm, prepared ground. Soft or wet ground needs six to eight, and often a layer of larger stone underneath to spread the load. The figure to check is that the stone is deeper than the deepest rut it has to bridge — a thin layer over soft ground disappears into it.

Should I order extra for compaction?

Yes — plan on 10% to 20% more than the calculated volume, and more again for a deep loose fill. Stone is bought and sold loose, and the layer you are left with after rolling is thinner than the layer you spread. A short load means a second delivery, which usually costs more than the extra stone would have.

Which gravel should I use?

Crushed stone is angular and locks together, which is exactly what a driveway base needs. Pea gravel is rounded and pleasant underfoot but migrates under wheels, so it belongs on a path or a playground rather than under a car. River rock is the largest and the lightest of the three, and it is what a drainage trench or a dry creek bed is lined with.

• Approximate Conversions from U.S. Customary Measures to Metric — the chart behind the short ton (2,000 lb) and cubic yard conversions used here — National Institute of Standards and Technology
• The International System of Units (SI) brochure — the tonne is 1,000 kg and is accepted for use with the SI, which is what makes a tonne 10% heavier than a short ton — Bureau International des Poids et Mesures (BIPM)