Rough to Finished Lumber Calculator

Rough to Finished Lumber Calculator for hardwood bought rough. Enter the rough size, milling losses and price to see the finished size, the usable wood and the cost per board foot.

Rough to Finished Lumber Calculator for Shop Milling

Rough hardwood is sold by the size it came off the saw, but you build with what is left after jointing, planing, ripping and trimming. The Rough to Finished Lumber Calculator works out that remainder, then shows what each usable board foot really costs. It helps anyone choosing between 4/4 and 5/4, sizing a lumber order, or checking whether dealer-surfaced stock is worth the price.

Enter the rough thickness, average width and length as sold, where 4/4 means 1 inch and 8/4 means 2 inches. Then set how many boards, the price per board foot and whether you mill at home or buy S2S. Thickness loss, width loss, end trim, defect loss and resawing sit in the accordion.

Each loss comes off the matching dimension, and the defect share comes off what remains. Board feet are counted on the finished size, then multiplied by the number of boards.

$$B{F}_u=\frac{(T-L_t)(W-L_w)(L-L_e)}{144}\times n\times \left(1-\frac{d}{100}\right)$$

T, W and L are rough thickness, width and length in inches, the L terms are the matching losses, n is the board count and d is the defect loss in percent. With the defaults, six 4/4 boards 6-1/2 inches wide and 8 feet long are billed as 26 board feet. They leave 15.86 usable board feet at 3/4 × 6 inches, so 39% of what you paid for never reaches the project.

What 4/4 Really Mills Down To

The default thickness loss of 1/4 inch reflects the usual outcome. Jeff Mack Supply, a lumber retailer, says 4/4 usually finishes near 3/4 inch and 8/4 near 1-3/4 inch. Forum reports show how much that moves with the board.

One Sawmill Creek member jointed and planed 5 foot lengths of 4/4 red oak and ended at 11/16 inch, and one board at 5/8. In a separate thread, another member regularly gets 7/8 inch from 4/4 unless a board is badly twisted or cupped.

The difference is often how long the board is when it meets the jointer, and members in both threads cut parts to rough length first. For the same curve, bow depth grows with the square of the length. A 1/4 inch bow over 8 feet drops to about 1/16 inch over 4 feet and 1/64 inch over 2 feet.

Less bow means less wood planed away to get a flat face. Set Thickness Loss to 1/8 inch for short, flat parts and 3/8 inch for long, twisted boards, and watch the finished size change.

Rough stock can also start fatter than its label. A sawyer on the TractorByNet forum describes saw scales that cut 4/4 at 4/4 plus 1/16 inch so it still planes to size after drying. Measure a few boards before trusting 1 inch.

Dealer S2S Versus Milling It Yourself

Switch Milling to Dealer S2S and the tool applies the surfacing allowance from the NHLA grading rules. Stock up to 1-1/2 inches loses 3/16 inch, so 4/4 arrives at 13/16. Thicker stock loses 1/4 inch, taking 8/4 to 1-3/4.

Width stays rough on S2S, so width loss defaults to zero in that mode. NHLA also measures surfaced lumber before surfacing, so you pay for 1 inch even though 13/16 arrives. The Rough to Finished Thickness Chart puts the dealer size beside your shop size for each thickness from 4/4 to 16/4.

S2S is not always flat. A member in the Sawmill Creek 4/4 thread points out that 13/16 inch S2S leaves only 1/16 inch to flatten a board. A member in another Sawmill Creek thread notes his yard's machine planes both faces at once, which does not remove twist.

Grade, Defects and the Real Price per Board Foot

Defect loss covers knots, checks, wane and sapwood you cut around. The presets come from the NHLA minimum clear-face cutting yields that the Wood Handbook's Chapter 6 summarizes. FAS must yield at least 83-1/3% clear cuttings, No. 1 Common 66-2/3% and No. 2A Common 50%.

The table runs the default six boards at $8 per board foot through each preset. Milling losses stay at the defaults, so only the defect share changes from row to row.

Those grade figures are minimums for the whole board, measured in cuttings of set sizes. The American Hardwood Export Council notes No. 1 Common allows clear cuttings as small as 3 inches by 3 feet or 4 inches by 2 feet. The grade figure is a floor, and how close your own yield comes depends on the part sizes you need.

The third and fourth cards turn the losses into an order. Rough BF per Usable BF tells you what to buy, so 100 usable board feet at the defaults means about 164 rough. The fourth card spreads the lumber bill over only the wood you keep, $13.11 per usable board foot against an $8 sticker price.

The Wood Whisperer's guide to calculating lumber bases rough 4/4 on a full 1 inch because that is how the yard charges. A reader there calls 15% to 20% extra the standard allowance and notes Chris Schwarz adds 50% to 100% for grain selection. To price rough stock by the dealer's own tally, use the Board Foot Calculator.

Resawing Thick Stock for Thin Parts

Set Resaw Into above 1 and each slice loses its share of the saw kerf plus its own thickness loss. Both faces of every slice still need planing, so the loss applies to each one.

$$t=\frac{T-(s-1)k}{s}-L_t$$

Here s is the number of slices and k the resaw kerf. An 8/4 board split in two on a bandsaw with a 1/16 inch kerf gives slices of about 23/32 inch after a 1/4 inch loss each. Split 5/4 the same way and each slice finishes near 11/32 inch.

The tool warns when slices finish under 1/8 inch, since thin slices can cup as internal stress releases. Letting them rest before final planing helps. The Kerf Spacing Calculator shows how blade choice changes what each cut consumes.

Choosing Between 4/4 and 5/4

Should I buy 4/4 or 5/4 for 3/4 inch parts?

Usually 4/4, if you pick flat boards and cut to rough length first. A Sawmill Creek member advises that 4/4 is normally milled to 3/4 and 5/4 to 1 inch, and that going up a size just throws away another 1/4 inch.

For 7/8 inch parts the answer shifts. On the Fine Woodworking forum, members report 7/8 from 4/4 only sometimes, 13/16 more often, and 5/4 when the stock is bowed or cupped. Run both thicknesses through the tool with your real losses and compare the cost per usable board foot.

Why is thin 3/4 inch rough stock billed as 1 inch?

Under NHLA rules, standard thicknesses below 1 inch are counted as 1 inch when board feet are tallied. So a rough board sold as 3/4 inch costs the same per board foot of surface as true 4/4 but holds less wood.

The tool bills stock under 1 inch at 1 inch and flags it. Buying true 4/4 usually gives more usable wood for the same money, as long as you have a planer to take it down.