If you have studied forestry or logging, looked into buying a sawmill, or sought to buy lumber in bulk, you’ve almost certainly seen the abbreviation “MBF” as a unit of measurement. MBF means “thousand board feet” and refers to the yield of board feet, in thousands, that can either be found in a quantity of sawn lumber or that can reasonably be derived from logs or standing timber. In forestry, the measurement of MBF is most commonly reserved for high-grade saw timber, whereas cords and tons are more common measurements for lower-grade products. In this article, we will dig into MBF, its uses, and what it measures. As it is one of the most important measures in forestry, sawmilling, and selling timber, it is crucial to understand.
What Is a Board Foot, and how does it relate to MBF?
The base unit of MBF is of course the “board foot.” To understand what MBF is, one must understand exactly what a board foot is. A board foot is a standardized measurement of a rough green board with the dimensions 12″x12″x1″, or 1/12 of a cubic foot. A model of a single board foot is visualized below together with a
An important distinction of a board foot is that, traditionally, it is both green (un-dried) and rough (un-planed). As lumber dries, it will shrink slightly, and the planing process can remove a substantial amount of volume, so measuring lumber or timber in board feet does not account for the loss of volume in these two processes. It only accounts for the loss of volume in milling itself.
When you see the
In Timber and Forestry, MBF Is a Measurement of Yield
In forestry, there is seemingly an endless list of units and measurements of volume that aren’t perfectly interchangeable, and MBF is yet another on that long list. However, most units, such as cubic feet and cords, are a unit of volume. Other units, like tons, are units of weight. Board feet and MBF are unique in that it is a measurement of yield. When MBF is used in timber sales, logging, and forestry, it is usually estimated using log rules, which are systems of estimating log yield based on predetermined assumptions regarding kerf and taper. This is an important differentiation, as kerf and slab wood can represent a substantial amount of gross volume inside a log. Put simply, logs are round, and boards are square, so there is bound to be geometric inefficiency. Measurements of board feet and MBF account for this.
In Lumber, MBF Is a Measurement of Gross Volume
When MBF is used in already-milled lumber, however, the situation is the exact opposite. MBF measures the gross volume of green, unplaned boards. When boards go through this process, volume is lost to shrinkage in the drying process as well as shavings in the planing process. MBF does not account for this loss of volume.
This is why famously 2×4 boards are not actually 2×4. The nominal dimensions refer to the board foot volume before the drying and planing process. The actual measurements of a 2×4 are 1.5×3.5.
This is not a technically true explanation, however. In actuality, the lumber standard for a 2×4 measures only the finished boards, so sawmills often cut smaller than 2×4 to begin with and end at the standard size as their mill equipment allows. In any case, sometimes it is just better to stick to the easier explanation.
How Many MBF Are in a Cord of Wood?
MBF and cords are not entirely convertible, if at all. A cord is defined as 128 cubic feet. Given the rule that a board foot is 1/12th of a cubic foot, then there should be about 1.5 MBF per cord. However, as any experienced sawmill operator can tell you, this is not the case. Because cords are a unit of volume and MBF expresses yield, a cord of wood will yield substantially less product than its gross volume due to kerf, slabs, and defect. A generally accepted rule of thumb is that there are about 500 board feet (or .5 MBF) in a cord of wood, assuming the cord is comprised of sawlog material. The true number will vary greatly depending on the size and quality of logs in the cord, so it should only be used for rough estimates. In fact, it is entirely possible to have 0 board feet in a cord due to the size or quality of wood in that cord. To truly determine the MBF in a cord of wood, one should scale logs individually.
How Many MBF Are in a Ton of Logs?
The same rules from estimating MBF in a cord apply to estimating weight. However, because we are now converting yield to volume and then to weight, a further assumption must be made as to the weight of the wood. Nonetheless, a good rule of thumb is that there are .2 MBF in a ton of softwood and .18 MBF in a ton of hardwood. The difference between the two comes from the difference in weight between the two species. Usually, hardwood weighs heavier than softwood, so there is going to be less MBF per unit of volume.
How to Convert MBF to Board Feet
Because MBF is merely an expression of one thousand board feet, converting MBF to BF is incredibly easy and readily convertible. To convert MBF to board feet, simply multiply MBF by 1000. The product of this equation will be the yield of lumber expressed in board feet.
How is MBF Price Calculated?
The price of lumber in MBF is largely determined by the grade and species of the log. That said MBF technically has three different prices at different points in the market: Stumpage, log, and lumber.
Stumpage prices are the price per log paid to the landowner once the timber is harvested. The stumpage price of saw logs is often expressed in MBF. You can find those prices in a list we have compiled here.
Log prices, on the other hand, are the price paid to loggers for logs delivered to the mill. Because this is the price paid by the party doing the milling, this is arguably the most commonly used and most important application of pricing MBF, and so an entire job title at the mill (log scaler) is dedicated to measuring and pricing these logs.
These prices can be found by contacting your local mill. They vary drastically from region, species, and mill.
Of course, MBF is also used to price lumber on the consumer side. Believe it or not the lumber that is traded on market commodity exchanges is priced in MBF. Next time you look up lumber prices, remember that those numbers refer to those little green, un-planed squares pictured above.