UKTC Archive

Re: Diameter callipers

Subject: Re: Diameter callipers
From: Simon Pryce Arboriculture
Date: Aug 14 2019 11:26:55
This is one way of doing it with a ruler, builder's tape and a surveyor's tape / range finder

Stand a measured distance from the tree, say 5m or 10m, which makes the arithmetic easier.  Farther from the tree makes it more accurate but realistically that won't matter for most arboricultural purposes.

Lock the tape so the rule sits on the ½m mark, hold out with the end of the builders tape just below the eye.  Sight on the trunk over the rule.  From 5m multiply the apparent diameter shown on the rule by 10, i.e. ½m divided by 5m.  From 10m multiply by 20 or use the 1:2 side of a scale rule and multiply by 10.

It's simpler than it sounds and quite quick with a bit of practice.  I use it mainly for off site trees.


A generous estimate is accurate enough for most purposes, particularly for RPAs. If the base of the tree is heavily overgrown it's not very likely that anyone else will check it.

Even if you can't get a tape round the tree it's still worth trying to see round the base as far as possible in case there are any defects.


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