Square feet measure area; board feet measure volume. Multiply the area you need to cover by the stock thickness in inches. At 1″ (4/4 rough) the numbers match one to one — 100 sq ft of coverage needs 100 BF before waste.
| Area | at 3/4″ | at 1″ (4/4) | at 1-1/2″ (6/4) | at 2″ (8/4) |
|---|---|---|---|---|
| 10 sq ft | 7.5 | 10.0 | 15.0 | 20.0 |
| 25 sq ft | 18.8 | 25.0 | 37.5 | 50.0 |
| 50 sq ft | 37.5 | 50.0 | 75.0 | 100.0 |
| 100 sq ft | 75.0 | 100.0 | 150.0 | 200.0 |
| 250 sq ft | 187.5 | 250.0 | 375.0 | 500.0 |
The classic mistake in area math is forgetting that boards lose width to their joints. A tongue-and-groove floor board sold as 4″ wide covers only about 3-1/4″ of floor once the tongue disappears into its neighbor — so 100 sq ft of room needs the coverage math done on face width, then converted to board feet on full width. Shiplap and V-groove paneling lose width the same way.
The second trap is waste on top of coverage: flooring installers order 8–10% over the room area for cuts and culls even after the face-width correction. For wainscoting a 10′ × 4′ wall, that compounding is the difference between finishing Saturday and a second trip to the yard.
Working up a whole order? The planner totals every part with waste and tax.