When you hear a woodworker ask for "five-quarter cherry" or "eight-quarter walnut," they're using the quarter system — the standard way hardwood thickness is specified in North America. Understanding this system is essential for ordering the right material for your project.
The Quarter System Explained
Hardwood lumber thickness is measured in quarters of an inch. The number before the slash tells you how many quarter-inches thick the rough lumber is:
| Notation | Pronounced | Rough Thickness | S4S Thickness |
|---|---|---|---|
| 4/4 | "four-quarter" | 1" (25mm) | 13/16" to 3/4" |
| 5/4 | "five-quarter" | 1.25" (32mm) | 1-1/16" to 1" |
| 6/4 | "six-quarter" | 1.5" (38mm) | 1-5/16" to 1-1/4" |
| 8/4 | "eight-quarter" | 2" (51mm) | 1-13/16" to 1-3/4" |
| 10/4 | "ten-quarter" | 2.5" (64mm) | 2-1/4" to 2-3/16" |
| 12/4 | "twelve-quarter" | 3" (76mm) | 2-3/4" to 2-11/16" |
Why Rough vs. Surfaced Thickness Differs
The quarter system refers to rough sawn thickness — the dimension of lumber as it comes off the sawmill. When lumber is surfaced (planed smooth), material is removed:
- Face jointing: Removes 1/16" to 1/8" per face to flatten
- Planing: Removes another 1/32" to 1/16" per face for smoothness
- Total loss: Typically 1/8" to 1/4" from rough to S4S
This is why 4/4 lumber (1" rough) typically finishes at 13/16" or 3/4" surfaced.
What Each Thickness Is Used For
4/4 Lumber (1" rough, 3/4" finished)
The most common thickness for:
- Cabinet face frames and doors
- Furniture panels and drawer boxes
- Shelving
- Interior trim and moldings
- Woodworking hobby projects
5/4 Lumber (1.25" rough, 1" finished)
Common for:
- Decking (especially cedar and treated pine)
- Tabletops where you want slightly more heft
- Exterior trim
- Handrails
6/4 Lumber (1.5" rough, 1-1/4" finished)
Used for:
- Table legs and furniture frames
- Thicker tabletops
- Stair treads
- Heavier shelving
8/4 Lumber (2" rough, 1-3/4" finished)
Selected for:
- Substantial table legs and posts
- Workbench tops
- Butcher block
- Resawing into thinner stock
- Turning blanks
Board Foot Calculation
Hardwood is sold by the board foot (BF) — a volume measurement equal to 144 cubic inches of wood. Think of it as a piece of lumber 12" wide × 12" long × 1" thick.
The Golden Rule: Always Use Nominal Thickness
When calculating board feet, always use the nominal (rough) thickness — never the actual surfaced thickness. This applies whether you're buying rough lumber or S2S/S4S:
| You're Buying | Nominal | Actual | Use This in Calc |
|---|---|---|---|
| 4/4 Rough | 1" | 1" | 1" |
| 4/4 S2S or S4S | 1" | 3/4" | 1" (not 3/4") |
| 8/4 Rough | 2" | 2" | 2" |
| 8/4 S4S | 2" | 1-3/4" | 2" (not 1-3/4") |
Why? Because surfacing is a service, not a discount. The wood started at 1" thick at the sawmill. Surfacing removed 1/4" — but that wood didn't disappear, it became sawdust. You're paying for the original 1" of lumber plus the surfacing service. Using actual thickness (3/4") would undercount your board feet and underpay for the material.
There are two ways to calculate board feet. Use whichever feels more natural:
Method 1: All Measurements in Inches
This is the easiest way to learn. Multiply thickness × width × length (all in inches), then divide by 144:
Board Feet = (Thickness" × Width" × Length") ÷ 144
Example 1 (4/4 lumber): A board that's 1" thick, 6" wide, and 72" (6 feet) long:
(1 × 6 × 72) ÷ 144 = 432 ÷ 144 = 3 board feet
Example 2 (5/4 lumber): A board that's 1.25" thick, 8" wide, and 48" (4 feet) long:
(1.25 × 8 × 48) ÷ 144 = 480 ÷ 144 = 3.33 board feet
Method 2: Length in Feet
If you're measuring longer boards, this shortcut saves a step:
Board Feet = (Thickness" × Width" × Length') ÷ 12
Example: A 6/4 board (1.5" thick) that's 8" wide and 10 feet long:
(1.5 × 8 × 10) ÷ 12 = 120 ÷ 12 = 10 board feet
Both methods give you the same result — use whichever is easier for the board you're measuring.
How to Order Lumber at Craftsmen Supply
When ordering hardwood in Tampa, specify:
- Species: "Cherry," "White Oak," "Hard Maple," etc.
- Thickness: Use the quarter system ("4/4" or "five-quarter")
- Grade: We stock FAS (First and Seconds) — the highest standard grade for hardwoods
- Surfacing: Rough, S2S, or S4S
- Quantity: In board feet
Example order: "I need 50 board feet of 4/4 FAS Cherry, S4S."
Want Your Material Ready to Build?
If you're new to woodworking or just want to skip the milling step, S4S (Surfaced 4 Sides) lumber is surfaced flat and smooth on all four faces — ready to cut and assemble. Our S4S guide explains when it makes sense to pay for pre-surfaced material and what to expect dimensionally.
Visit us at 1605 N. 23rd St, Tampa, FL 33605, or call (813) 988-4677 to check stock and pricing.