Gravel Under Deck Calculator
The ground under a deck stays damp and shaded, so weeds and mud take over unless it is covered. The usual fix is woven landscape fabric with two to three inches of stone on top. This works out the stone in tons, cubic yards and bags for your deck's footprint, the fabric strips and rolls, and the edging to keep the stone in, with a cost range for the stone.
Why put gravel under a deck
The ground under a deck gets just enough light for weeds and not enough sun to dry out. Bare soil turns to mud, splashes the posts and holds moisture against the framing. A layer of woven landscape fabric with two to three inches of stone on top blocks the light, drains the rain that falls between the boards and keeps the underside clean enough to use for storage.
Worked example: 12 × 16 ft deck
| Step | Working | Result |
|---|---|---|
| Area | 12 × 16 | 192 sq ft |
| Volume at 3 in | 192 × 3 ÷ 12 ÷ 27 | 1.78 yd³ |
| +10% allowance | 1.78 × 1.1 | 1.96 yd³ |
| Pea gravel by weight | 1.96 × 1.35 | 2.64 tons |
| Fabric | 12 ft ÷ 2.5 ft per strip (3 ft roll, 6 in overlap) | 5 strips × 16 ft = 80 ft, 1 roll |
Which stone
- Pea gravel is smooth and comfortable to walk on and costs little, but it rolls on a slope.
- #57 crushed stone locks in place and drains best — the choice for sloped or wet ground. Size it with the #57 stone calculator.
- River rock is the decorative option where the underside of a low deck is on show; see the river rock calculator.
- Avoid crusher run here: the fines hold water against posts and footings.
Laying it
- Clear the vegetation and rake the soil so it falls away from the house.
- Lay woven fabric in strips with 6 in overlaps, pinned every 3 ft; cut neat openings around each post (the landscape fabric calculator counts staples).
- Spread the stone 2–3 in deep, keeping it at least 6 in below the joists so air moves under the deck.
- Edge any open side so the stone stays put.
Still planning the deck itself? Price it with the deck cost calculator, and for a low floating deck count the precast blocks with the deck block calculator.
Get the Gravel & Stone Calculator app for Android
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Frequently asked questions
- How much gravel do I need under a 12x16 deck?
- About 2.6 tons of pea gravel at 3 inches deep with a 10% allowance: 192 square feet at 3 inches is 1.78 cubic yards, 1.96 with the allowance, and pea gravel weighs about 1.35 tons per yard. That is roughly 106 bags of 0.5 cubic feet, so bulk delivery is far cheaper.
- What is the best gravel to put under a deck?
- Pea gravel if you will walk or store things under the deck, because it is smooth underfoot, or #57 crushed stone if the ground is sloped or wet, because the angular pieces lock and drain. River rock looks best where the underside is visible. Avoid crusher run: its fines hold water against the posts.
- How deep should gravel be under a deck?
- Two to three inches over woven landscape fabric is enough to block light and keep weeds down; go to four inches on wet or uneven ground. More depth adds cost without much benefit, and the stone should always stay well below the joists so air can move under the deck.
- Should I put landscape fabric under the gravel?
- Yes. Woven fabric stops weeds from growing up through the stone and keeps the gravel from sinking into the soil. Overlap the strips by six inches, pin them every three feet, and cut neat openings around each post and footing.
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