Up until the 1908 Act allotment plots were normally 20 rods (or poles) and ranged from this one eighth of an acre to 4 acres in size (i.e. 640 rods/poles). The 1908 Act led to these smaller plot sizes to differentiate them from smallholdings.

Plot sizes are measured in rods, an old Anglo-Saxon unit so-called because it was the length of the rod used to control a team of eight oxen.

A rod is 5.5 yards (5.03 metres).

1 pole = 1 rod = 1 perch = 16 ½ feet.

A chain = 4 rods = 22yd (20.12m) and is the length of a cricket wicket.

A furlong = 10 chains.   A mile = 8 furlongs.

An acre is the area of land that could be ploughed in a day, being a furrow long (furlong)and a chain wide, or 160 square rods.

So in 1908 the standard size for an allotment became 10 rods

A 10 rod allotment is 10 square rods in area, 10 x 5.5 x 5.5 = 302.5 sq yd (253 sq m).

In metric units, a 10 rod allotment is one fortieth of a hectare: in imperial units it is one sixteenth of an acre.

Of course, the principle behind the average plot size no longer holds water, so local authorities, faced with a legal obligation to provide allotments and with lengthy waiting lists in some areas, have halved the traditional 10 rod plots to 5 - an area of 151.25 sq yards, or 126.5 sqm.  There are even reports that a London council have reduced some plots, available to novice gardeners, to 1.5 rods; and this is bound to cause problems with crop rotation as well as increasing the rist of pest and disease infestation for neighbouring allotments.

Thus you have to decide if you are going to model full size allotments on your layout, or if you are going to compress these in the same manor you compress your railway scenes.