Logs are offered for numerous possible uses and are usually delivered in layers. A specific room measure is used to calculate the amount of wood: the cubic metre. How it is calculated is explained in this article.
In a nutshell
- fm is a measure for determining 1 m³ of round wood without gaps
- Huber's formula is used for this
- fm can be calculated with or without bark
- is used as a comparison value
Solid meters: definition
The solid cubic meter (fm) is a special spatial dimension that is only used for round timber. The fm describes the amount of solid mass in a cubic meter, whereby the gaps (air spaces) are not included in the calculation. The measure is used exclusively for unprocessed logs that are available either as a whole trunk or as individual trunk pieces. Since the gaps are not part of the determination, fm is more of a comparative value for determining wood prices. It is divided into three variants:
- storage solid meter (vfm)
- Harvest meters (efm)
- Layer solid meter (sfm)
The storage cubic meter is used most frequently and describes the wood with bark. On the other hand, up to 10 percent is deducted for the loss of the bark in the harvest meter. Depending on the tree species, other values must be used here, for which special lists are available. The layer solid meter is an exception, as it describes layered firewood and split logs that contain very few air spaces. No matter which variant it is, they are always calculated in the same way. This will be addressed in the next section.
Notice: The cubic meter (rm) is derived from the fm, which is most frequently used in the trade in firewood and timber and corresponds to 1.4 to 2.0 fm, depending on the type of wood and processing. In contrast to the fm, it is a cubic meter of wood with spaces in between, which is significantly more accurate than an fm for the end user.
Solid meter: formula and application
To calculate the fm you need a formula. This makes it easier for you to calculate the amount of wood based on the available logs. The mathematical theorem used is derived from the classic volume calculation of a cylinder (height x base area) and how these fit into a cubic meter. The following values are required for this:
- F or fm: solid meters as a result
- d: mean trunk diameter in m
- L: trunk length in m
- Pi: number of circles
Based on these values, you can use the following mathematical theorem, Huber's formula, to determine the fm, which we will clarify again using the graphic:
d² x L x Pi/4 = F
Do not worry. At first glance, this sentence seems more complicated than it is. An example illustrates the application and the simple calculation method. For the example, a trunk with a length of 6 meters and a trunk diameter of 30 centimeters is assumed:
0.3² x 6 x pi/4 = 0.42F
As a result, the given trunk would have a volume of 0.42 fm. This allows you to effectively calculate how much wood is available per cubic meter per log. Yes, theoretically you have to calculate each individual trunk to determine their fm. For this reason, layered logs are marked in the forest. The mark stands for the fm. The result becomes more accurate the more the logs resemble an exact cylinder. The more uneven the trunk is, the more deviations you have to reckon with. This is characteristic of the fm.
Notice: If you don't have an option for Pi on your calculator, use the value 3.1416. This has established itself as the standard and allows the calculation of the solid meter without much effort.
frequently asked Questions
What is the bulk meter?The bulk meter is another way of measuring wood. The loose volume meter (SRM) describes the amount of wood poured in one cubic meter including the spaces in between. The bulk meter can only be calculated very vaguely, since the exact amount cannot be determined directly. The rule of thumb is: 1 loose meter corresponds to about 0.4 to 0.5 fm. The value depends on the type of wood and the way it is processed.
Should lumber be purchased in fm or rm?It makes sense for the consumer to buy logs in rm. An rm gives you a much better indication of how much material you're getting because the spaces have been factored into the calculation. In addition, ready-to-use logs are sold via rm, while fm is used for calculations of the general price of wood, which determines rm. For this reason, it is recommended to purchase quantities of wood in the rm.
Which wood products are not offered via the fm?Wood products that have already been processed are not calculated using the fm, but in kilograms or, more rarely, tons. The best example of this are wood briquettes, which are only offered in these dimensions. Vendors sometimes sell firewood or other logs by the kilogram, but this can vary widely. Here it depends on the provider.