Gravel Calculators

French Drain Gravel Calculator

A French drain is a trench: length × width × depth of the hole you dig, not the lawn above it. Pre-set to washed #57 stone — the drainage grade — at a 12" × 18" trench profile.

Step 1 · Trench area
Step 2 · Trench dimensions
Step 3 · Drainage stone

The stone in the list marked "avoid" is there for comparison — fines wash into pipes.

How the trench math works

The whole trench gets filled with stone (pipe displaces a little — see note below), so volume is simply length × width × depth of the trench. A 50-foot run, 12 inches wide and 18 inches deep: 50 × 1 × 1.5 = 75 ft³ = 2.78 yd³ of washed #57 ≈ 3.7 tons.

The pipe subtracts less than you'd guess: 50 feet of 4" pipe displaces only ~4.4 ft³ (about 6% of that trench) — most people just let it be part of the safety margin.

Water moves through voids, not stone. That's why fines are the enemy here: crusher run compacts into something nearly solid, and washed-in dust gradually seals a drain. Washed #57 (or larger) keeps open channels, and a filter fabric wrap keeps soil out for years. Slope the trench about 1" per 8–10 ft of run toward its outlet.

Gravel Calculator

Any area, any material — the general tool.

Retaining Wall Gravel Calculator

The other drainage job: backfill behind a wall.

Gravel Types and Sizes Guide

Why washed stone drains and dense-graded stone doesn't.

Gravel Calculator (Tons)

Plain tonnage with the density table.

French drain FAQ

What size gravel for a French drain?

Washed #57 stone (about ¾ inch) is the standard choice — large enough for water to move through quickly, small enough to surround the perforated pipe. Never use crusher run or anything with fines: fines wash into and clog the pipe.

How wide and deep should a French drain trench be?

A typical residential trench is 12–18 inches wide and 18–24 inches deep, holding a 4-inch perforated pipe on a bed of stone with stone covering it. Enter your actual trench dimensions — volume comes straight from the trench, not the ground above it.

How much gravel do I need for a 50 foot French drain?

A 50-foot trench, 12 inches wide and 18 inches deep, is 75 cubic feet — about 2.8 cubic yards or roughly 3.7 tons of washed #57 stone. The calculator gives exact figures for your dimensions.