Pallet tolerances: allowed variation in size, flatness and squareness

Every pallet drawing is a target. Lumber moves, saws wander and nailing machines have play, so a spec also needs to say how far the real pallet may differ from the drawing. Without stated tolerances, "out of spec" is a matter of opinion.

The figures below are from the 2012 edition of the Uniform Standard for Wood Pallets, the edition that is publicly readable. Later revisions exist and may differ, so cite the edition in your spec.

Component (manufacturing) tolerances

The standard also sets a statistical rule: at least half of the pieces must meet or exceed the target size, and two standard deviations of the distribution must fall within the tolerance. A mill cannot run everything at the bottom of the range.

Assembly tolerances

Worked example: what "48 x 40" allows

For a GMA-style 48 x 40 stringer pallet built to these tolerances:

• Length: 47-1/2 to 48-1/4 in
• Width: 39-1/2 to 40-1/4 in
• Height: the stack is 5/8 + 3-1/2 + 5/8 = 4.75 in nominally. Each of the three parts may vary by 1/16 in, so the worst case stack-up is plus or minus 3/16 in: 4-9/16 to 4-15/16 in.
• Top boards: each 5/8 in board may be 9/16 to 11/16 in thick. A 3-1/2 in interior board may be as narrow as 3-1/4 in.
• Lead boards: within 1/4 in of flush with the ends.
• Notches: the 9 in length may be 8-7/8 to 9-1/8 in, and the notch may start anywhere from 5-5/8 to 6-3/8 in from the stringer end.

If your automated line or rack needs tighter numbers, state them explicitly. Automated storage in particular often needs a tighter flatness and height tolerance than the standard.

Moisture and shrinkage

Tolerances apply at the time of manufacture. Green lumber then shrinks as it dries: roughly 1% in dimension for each 5% drop in moisture content below about 28%. A published PDS example shows a 5/8 in deckboard shrinking about 0.014 in, and a 5-1/2 in board about 0.123 in in width, when drying to 19% moisture content. That can take a pallet that measured in tolerance at the mill slightly under size at the customer.

If size matters at the point of use, either specify kiln-dried lumber or state that tolerances apply at manufacture. See moisture content and green lumber.

Defect limits are separate

Tolerances control dimensions. Lumber defects (knots, wane, splits, decay, slope of grain) are controlled by the grade rules, which differ for reusable and single-use pallets. See reusable vs single-use pallets and lumber grades.

How to write tolerances into a spec

1. Name the standard and edition, for example "Uniform Standard for Wood Pallets, manufacturing and assembly tolerances".
2. Add any tighter limits your operation needs (flatness, height, fork opening).
3. Say when tolerances apply (at manufacture or at delivery).
4. Define how you will measure and sample, and what happens to out-of-tolerance loads.

How ISO and EPAL handle tolerances

ISO 6780 sets principal dimensions and tolerances for its six international footprints, and licensed EPAL pallets are built to EPAL's own technical specification. If a pallet must meet one of these, reference that document rather than the Uniform Standard. See ISO 6780 and EPAL.

palletdesign.ai dimensions every part at its actual size on the drawing, which is the size tolerances are measured against. See how to read a pallet drawing.