How to Calculate Crushed Stone Needed — Step by Step

The formula, in one paragraph

Calculating crushed stone is five steps. Measure the length and the width in feet and the depth in inches, then turn the depth into feet by dividing by 12. Multiply the three together for the volume in cubic feet. Divide by 27 for the cubic yards, because a cubic yard is 27 cubic feet and stone is sold by the cubic yard. Multiply the cubic feet by the density of your stone for the weight in pounds — crushed stone is 100 lb per cubic foot — divide by 2,000 for the tons, and divide the pounds by 50 and round up for the 50-lb bags.

Step 1: Measure the length, width, and depth

Start with the area. The example is a patio base 10 ft long and 12 ft wide, 4 in deep. Measure at the deepest point. The area is 10 × 12 = 120.00 sq ft.

Step 2: Turn the depth into feet and find the volume

The depth is in inches and the rest is in feet, so divide by 12 first: 4 in ÷ 12 = 0.33 ft, a third of a foot. Then multiply: 10 × 12 × 0.33 = 40.00 cu ft. That is the loose, uncompacted volume.

Step 3: Work out the cubic yards

A cubic yard is 3 ft by 3 ft by 3 ft, which is 27 cubic feet, so divide the cubic feet by 27: 40.00 ÷ 27 = 1.48 cu yd. Stone is sold by the cubic yard, usually in whole or half yards, so order 1.5 or 2 cu yd rather than 1.48 — a short load costs more in a second delivery than a little extra stone.

Step 4: Work out the weight and the tons

Multiply the cubic feet by the density of the stone you are buying: crushed stone is 100 lb per cubic foot, pea gravel 96, river rock 104, and limestone screenings 110. At the defaults, 40.00 × 100 = 4,000.00 lb. A ton is 2,000 lb, so 4,000.00 ÷ 2,000 = 2.00 tons. The same hole in pea gravel weighs 3,840.00 lb (1.92 tons), in river rock 4,160.00 lb (2.08 tons), and in screenings 4,400.00 lb (2.20 tons).

Step 5: Work out the bags, and check the answer backwards

Divide the pounds by 50 for the 50-lb bags and always round up: 4,000.00 ÷ 50 = 80 bags exactly. Pea gravel for the same hole is 3,840.00 ÷ 50 = 76.8, so 77 bags; river rock is 4,160.00 ÷ 50 = 83.2, so 84 bags. Then check backwards. If you already have 3 tons of crushed stone for a 10 × 12 ft area, the depth is 3 tons ÷ 100 lb per cubic foot ÷ 120 sq ft × 12 = 6.00 in: 3 tons is 6,000 lb, which is 60 cu ft, over 120 sq ft. And 2 tons at 4 in deep covers 120.00 sq ft: 2 tons is 4,000 lb, which is 40 cu ft, at a third of a foot deep.

When the job is bigger, or the stone is different

A 20 × 15 ft driveway at 6 in deep takes 150.00 cu ft (5.56 cu yd, 15,000.00 lb, 7.50 tons, 300 bags), and a 30 × 20 ft driveway at 6 in takes 300.00 cu ft (11.11 cu yd, 30,000.00 lb, 15.00 tons, 600 bags) — at that size, order by the truckload, not by the bag. A thin 2 in top-dressing on an 8 × 8 ft patch takes only 10.67 cu ft (0.40 cu yd), but it still weighs 1,066.67 lb (0.53 tons), or 22 bags: stone is heavy even in small amounts.

What one cubic yard weighs

One cubic yard of crushed stone is 27 × 100 = 2,700.00 lb, which is 1.35 tons. One cubic yard of pea gravel is 27 × 96 = 2,592.00 lb, which is 1.30 tons. Remember that a cubic yard is a volume, not a weight: the same yard weighs a different amount for every stone, and a wet load weighs more than a dry one.

What NOT to do

Do not order exactly what the formula gives: add 5–10% for waste, spillage, and uneven ground, and round the yards up to the nearest half yard. Do not use the loose volume for a compacted base: compacting squeezes the stone thinner, so a compacted base needs more stone. Do not forget the bags round up: 76.8 bags is 77 bags, not 76. Measure the depth at the deepest point, and check the density with your supplier, because a wet load weighs more than the standard 100 lb per cubic foot.

That box is the whole formula.