What makes a quality log for timber purchase?

When we are looking at the quality of timber we take three things into consideration: Size, height and limbs.

Size

When we refer to the size of a tree, we refer to the diameter. Measuring through the tree, not around the tree, is known as diameter waist height (DWH). The bigger the DWH, the better. When we refer to the size of the log, we are referring to the top end, and measuring the narrowest point inside the bark. The minimum diameter of a log generally has to be 9–10 inches on the small end, depending upon the market. Typically, a log tree has a DWH of 12–14 inches and greater.

Below are some examples:

This tree has a massive 24-inch DWH but is not suitable for a log because it doesn’t have the height, and the limbs are too near the ground.		This 16-inch diameter tree would barely cut a 17-foot log. The mills would prefer not to receive a log like this but a few are ok. A load of logs like this would be downgraded to pulpwood.
Short Log Tree This is an awesome log tree. It is about 20 inches in diameter, but all it will cut is a 25-foot log.		Tall Log Tree This tree is just about as good as it gets. The form class is great. It hardly tapers any as it extends up. This tree is about 18 inches in diameter and will easily cut two 35-foot logs and still be a 10- to 11-inch log.

Height

The taller the tree, the more likely it will cut into more logs. Your tree may be so big that you can’t wrap your arms around it, but if it doesn’t grow 25-feet tall it doesn’t make a good log.

Limbs

All trees grow limbs; some are just a short distance off the ground. A tree can be very large in diameter and be very tall, but if it has limbs near the ground, it doesn't make a good log. Mills don’t like a lot of limbs on a log because where there's a limb, there is a knot behind it. And a knot in lumber is a weak spot.

Some more examples:

No good.		No good.
No good.		No good.		Awesome cedar log!

The bigger the tree, the less logs it takes to make a load.

The taller the tree, the more logs we get and the less trees to make a load.

The shorter the tree, the less logs we get and the more trees to make a load.