How do you calculate trench volume?

Length × width × depth, all in feet, divided by 27 for cubic yards. A trench 100 ft long, 18 in wide and 36 in deep is 100 × 1.5 × 3 = 450 cu ft, or 16.7 cubic yards.

How much gravel do I need to bed a pipe?

Multiply the trench width and length by the stone depth (bedding under the pipe + the pipe + cover over it), then subtract the pipe's own volume. For 100 ft of 4 in pipe in an 18 in trench with 4 in under and 6 in over, that is about 6.2 cubic yards, roughly 8.6 tons of #57 stone.

Why is my spoil pile bigger than the trench?

Soil swells when it is dug because the packed grains loosen. Common earth takes up about 25% more room in the pile, clay more. That matters when you size a dumpster or count truckloads.

When does a trench need shoring?

OSHA requires a protective system — sloping, shoring or a trench box — for trenches 5 feet deep or more unless they are entirely in stable rock (29 CFR 1926.652). From 4 feet, a ladder or ramp must be within 25 feet of travel.

How wide should a trench be for a 4 inch pipe?

Usually 12 to 18 inches: wide enough to place and bed the pipe and compact stone along its sides. Deeper trenches that people work in must be wider to be dug and protected safely.

Drainage & Base

Trench Calculator

A trench is three jobs: digging the soil out, bedding the pipe in stone, and putting soil back. This calculator measures each one — the cubic yards you excavate, how much that soil swells in the spoil pile, the stone for the pipe zone (minus the pipe itself), the soil that goes back and the surplus left over — in imperial or metric.

Next calculatorGravel Delivery & Truck Load CalculatorHow many truckloads haul the spoil or bring the stone.

Trench volume per 100 feet

Width × depth	Excavated	Spoil pile (+25%)	4 in pipe bedding stone
12 × 18 in	5.6 yd³	6.9 yd³	4 yd³ (5.6 tons)
12 × 24 in	7.4 yd³	9.3 yd³	4 yd³ (5.6 tons)
18 × 24 in	11.1 yd³	13.9 yd³	6.2 yd³ (8.6 tons)
18 × 36 in	16.7 yd³	20.8 yd³	6.2 yd³ (8.6 tons)
24 × 48 in	29.6 yd³	37 yd³	8.3 yd³ (11.6 tons)

Volume is length × width × depth. The stone column fills the pipe zone — 4 in under a 4 in pipe and 6 in over it — and subtracts the pipe itself, using washed #57 stone at 1.4 tons per cubic yard. Metric users can switch units above; results show m³ and metric tonnes alongside.

Bank, loose and compacted soil

Soil in the ground is "bank" measure. Dug out, it loosens and swells — about a quarter more for ordinary earth, up to 40% for clay — so the spoil pile and the number of truckloads are bigger than the hole. Put back and compacted in thin lifts, it shrinks again. Because the stone and pipe take up part of the trench, there is always soil left over; the calculator shows how much to haul away or spread.

Digging safely

Call 811 first. Utilities are marked for free a few days after you call, and hitting a gas or power line is the biggest risk in any trench.
5 ft and deeper: OSHA requires a protective system — sloping, benching, shoring or a trench box — unless the trench is entirely in stable rock (29 CFR 1926.652(a)(1)).
4 ft and deeper: a ladder, stairway or ramp must be within 25 ft of travel for anyone in the trench (29 CFR 1926.651(c)(2)).
Keep the spoil pile at least 2 ft back from the edge (29 CFR 1926.651(j)(2)) so it can't slide back in.

Draining water away? Size the stone and fabric with the French drain calculator or price the whole job with the French drain cost calculator. Leftover soil can level a low spot — see the fill dirt calculator.

Get the Gravel & Stone Calculator app for Android

Estimate gravel, stone, sand, and mulch on the job site, save projects, and share quantities with your supplier.

Get it onGoogle Play

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Frequently asked questions

How do you calculate trench volume?: Length × width × depth, all in feet, divided by 27 for cubic yards. A trench 100 ft long, 18 in wide and 36 in deep is 100 × 1.5 × 3 = 450 cu ft, or 16.7 cubic yards.
How much gravel do I need to bed a pipe?: Multiply the trench width and length by the stone depth (bedding under the pipe + the pipe + cover over it), then subtract the pipe's own volume. For 100 ft of 4 in pipe in an 18 in trench with 4 in under and 6 in over, that is about 6.2 cubic yards, roughly 8.6 tons of #57 stone.
Why is my spoil pile bigger than the trench?: Soil swells when it is dug because the packed grains loosen. Common earth takes up about 25% more room in the pile, clay more. That matters when you size a dumpster or count truckloads.
When does a trench need shoring?: OSHA requires a protective system — sloping, shoring or a trench box — for trenches 5 feet deep or more unless they are entirely in stable rock (29 CFR 1926.652). From 4 feet, a ladder or ramp must be within 25 feet of travel.
How wide should a trench be for a 4 inch pipe?: Usually 12 to 18 inches: wide enough to place and bed the pipe and compact stone along its sides. Deeper trenches that people work in must be wider to be dug and protected safely.