Nominal 4×4 → Actual 3½" × 3½"

What size is a 4×4, really?

Q: What size is a 4×4, really?

A nominal 4×4 actually measures 3½" × 3½". The difference comes from milling and drying — the board starts closer to its named size, then shrinks as it's surfaced smooth and dried to standard moisture content.

A 4×4 is sold and labeled as 4×4, but it actually measures 3½" × 3½". The difference comes from milling and drying — the board starts closer to its named size, then shrinks as it's surfaced smooth and dried to standard moisture content.

DASHED = WHAT IT'S CALLED · SOLID = WHAT YOU GET

A 4×4 is actually 3½" × 3½" — not 4×4.

What a 4×4 is actually used for

Deck posts, fence posts, small structural posts

Good to know before you buy

Pressure-treated rated for ground contact is a different (and more expensive) product than 'above ground' PT — check the end tag if any part of the post touches soil or concrete.

How many 4×4s do you need?

USES ACTUAL WIDTH, NOT NOMINAL

Boards to span a width

Calculates how many 4×4 boards, laid edge to edge, are needed to cover a given width — using the real 3½" width plus any gap you leave between boards.

Width to cover (ft)

Gap between boards (in)

Board feet

Uses the actual 3½" × 3½" dimensions to calculate true board feet for pricing or ordering.

Length (ft)

Quantity

4×4 vs. every other size

FULL REFERENCE CHART

Nominal Size	Actual Size	Actual (decimal)

Other sizes

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