Deckboard thickness and spacing: how to lay out a pallet deck

The deck is the part of a pallet the load actually touches. Its board thickness decides how much the deck bends between stringers or blocks, and its spacing decides how well cartons, bags and drums are supported. Most deck problems, from boxes sagging into gaps to boards snapping at the lead edge, come from getting one of these wrong for the load. This guide gives the common sizes, the spacing arithmetic, and how to choose.

#Common deckboard sizes

Deckboards are stated as thickness × width × length, in actual dimensions. On a stringer pallet, deckboard length equals pallet width.

The Uniform Standard for Wood Pallets allows single-use lumber quality only when deckboards are at least 5/8 in thick (and stringers at least 1-1/4 in wide), which is one reason 5/8 in is so common.

#Lead boards

The lead board is the outermost deckboard at each end. It takes fork impacts and carries the load at the pallet edge, so it is usually wider than the interior boards (5-1/2 in or more) and gets more nails. Some designs double it with a second board butted against it. Wider lead boards also give pallet jacks and racks more bearing at the edge.

#How to calculate deckboard spacing

Most decks put the two lead boards flush with the pallet ends and space the interior boards equally.

gap = (pallet length − sum of board widths) ÷ (number of boards − 1)

GMA-style 48 × 40 top deck: 2 boards at 5-1/2 in and 5 at 3-1/2 in.

• Sum of widths: 2 × 5.5 + 5 × 3.5 = 28.5 in
• Gap: (48 − 28.5) ÷ 6 = 3.25 in
• Board leading edges: 0, 8.75, 15.5, 22.25, 29, 35.75 and 42.5 in

Other counts on a 48 in pallet, with two 5-1/2 in lead boards and 3-1/2 in interior boards:

The designer flags top-deck gaps over 5 in as a risk for sagging cartons and bags.

#Bottom deck spacing

Bottom boards follow different rules because they must clear the stringer notches and let pallet jack wheels reach the floor.

• On a notched stringer pallet, the interior bottom boards are grouped between the notches. On the GMA-style design, three 3-1/2 in boards sit at 15, 22.25 and 29.5 in with 3.75 in gaps, and the openings next to the lead boards are 9.5 in wide over the notches.
• On block pallets, the bottom style (perimeter, cruciform or unidirectional) sets the layout.
• On pallets for conveyors, bottom boards must run in the right direction and be close enough to bridge the rollers. See pallets for automation.

#How thickness and span affect strength

A deckboard is a small beam spanning between stringers or blocks. On a 48 × 40 pallet with three 1-3/8 in stringers, each span is about 17-15/16 in clear.

These ratios follow from beam theory for the same species and grade. The actual safe load depends on the whole pallet, the connections and the support condition, and should come from the manufacturer's analysis. Deckboards govern capacity when a pallet is racked across its width, when loads are concentrated between stringers, and at the lead boards under fork impact. See pallet racking and deflection.

#Choosing spacing for the load

The rule of thumb: nothing on the deck should be able to bridge a single gap with an unsupported wall or corner. See unit load design.

#Nails and thickness

Thicker boards need longer nails. The Uniform Standard calls for at least 1-1/4 in of penetration into the stringer or block (1 in if the deck is 1/2 in or thinner). So:

Boards up to 5-1/4 in wide need at least 2 nails per joint; 5-1/4 to 7 in wide need 3. See pallet nails and fasteners.

#Deckboard defects that matter

Thickness and spacing only work if the boards are sound. The Uniform Standard's lumber quality rules limit knots, wane, splits and decay, with tighter limits for reusable pallets than single-use ones. On the deck, watch for:

• Wane (missing wood at the board edge) on the top face, which reduces bearing and can snag packaging;
• Knots near nail joints, which weaken the connection;
• Splits at board ends, which grow with every fork impact;
• Thickness variation between boards, which makes the deck uneven for automation and palletizers.

Specify a grade and a thickness tolerance for decks that support fragile loads or run through automated equipment. See pallet lumber grades.

#Cost trade-offs

Board feet drive wood pallet cost. Adding a 3-1/2 in × 5/8 in × 40 in top board adds about 0.61 board feet. Going from 5/8 in to 3/4 in on all 12 deckboards of a GMA-style pallet adds about 1.7 board feet. Compare options with the board feet calculator or in the designer, which updates spacing, board feet and weight as you change the count and thickness.