Measuring the Perimeter or Girth of a Rectangular building

fig 1

A rectangular plan of a building with the length = 15,000mm and width = 6,000mm and wall thickness of 300mm.
It important to first note if the dimensions for a drawing are given from “out-to-out” or “in-to-in”.

The formula for finding the Girth is
2(L + W) ± 4(T) + 2r
If the dimensions are out-to-out then the formula turns
2(L + W) - 4(T) + 2r
If the dimensions are in-to-in then the formula turns
2(L + W) + 4(T) + 2r

Where L is the length (most times the longest side) of the building
            W is the width of the building
            T is the wall thickness
            r is the length of recess (is used only in the presence of a recess).
Based on the example fig 1 the dimensions are both Out-in-out
Therefore, the girth can be calculated thus;
Note: convert dimensions to metres.
Thus:   L = 15,000mm = 15.00m
            W = 6,000mm = 6.00m
            T = 300mm = 0.3m
Thus,
Girth = 2(L + W) – 4(T) for out-to-out
            = 2(15.00 + 6.00) – 4 (0.30)
            = 2(21.00) – 1.2
            = 42.00 – 1.2
            = 40.8


Thus girth or perimeter is 40.8mm
Note: the girth is usually taken as the length of the center line.