### Another odd use of percentages - wood moisture

In case you're ever involved in a discussion about the moisture content of wood:

Moisture content of wood is the weight of the water relative to the dry weight of the wood expressed as a percentage.

e.g. if it's 100% moisture content, it means there's as much water (by weight) as there is wood fiber. If you took a sample, weighed it, then stuck the sample in an oven for several hours until it was completely dry, it would weigh 1/2 what it did when it's wet.

So it's quite possible to have 200% moisture content in wood - it's got twice as much water as wood. Typical numbers for "green" lumber are 40-60%, dry lumber is more like 18-28%.

Ward
June 5th, 2008 2:00pm

Well, that's reasonable since it's probably unrealistic to have an accurate measure of the saturation point of wood, especially when there are so many different types of wood.

The funny thing about all this is that there is nothing special about percentages. All percentage means is "parts per hundred". Another way of putting it is "times 100 with % on the end".

So any number which can be thought of as a ratio or fraction can be made into a percentage by multiplying it by 100.

Thus we have 0.5 is 50%, 1.1 is 110%, 5 is 500%, and so on.

In the wood example, there are two equivalent statements:

"The moisture content of this wood is one fifth of the dry weight."

"The moisture content of this wood is 20% of the dry weight."

Using dry weight as the reference makes lots of calculations easier actually.

bon vivant
June 5th, 2008 2:10pm

It's kind of amazing how much water wood holds. My dad just had an oak or two sawed up into planks. It has to be dried outside, because if he brought it inside it would rust everything in his shop (and he has a huge shop).

If you think about it, trees move tons of water from below ground to way up high, without a motor. Amazing...

LeftWingPharisee
June 6th, 2008 6:44am