(Not very scientific, serves no real world purpose and should not be taken as an accurate method of calculating board feet content of a log.)
Log rules are designed to be used with certain tree shapes, calculating for specific lengths, they could include waste of cutting or designed to cut to certain board sizes. Some of these rules are used in various locations, some are used regional and then there are those that are designed to work for just one mill.
With this in mind, you can get very different results for the various rules that used for estimating the board feet content of logs.
Some rules require diameter measurements taken from the small end and others will have to be from mid length or an average of small end and large end of the log. To keep it simple this calculator uses an average diameter for all.
Included is Spike's cubic foot calculation for the log to estimate the cubic foot volume and a conversion to cubic metres.
Brereton sticks out as a sore thumb. This is because this rule is based on cubic feet *12 = board feet