If you have ever seen the term “Cunningham Acre” or “Scottish Acre” (also seen as Scots Acre) in your Irish research, then you no doubt raised an eyebrow. This was a land measurement brought over from Scotland where it had been the standard measurement since 1661. In Scotland it was replaced by the English Acre in 1824. In historic Ireland, it continued until the Ordnance Survey technically replaced the Cunningham (Scottish) Acre with the English Acre by the mid-1830s. However, in reality, its usage survived into the twentieth century in places such as eastern County Down.
You will see the Cunningham (Scottish) Acre mostly in the deeds, leases, and landlord estate records for Ulster. It is sometimes seen as “Conyingham Acre.” It will usually state the type of acres in the record. For the most part, you can assume most records are in English Acres or Irish Acres outside of Ulster, even if it is not stated. From my experience, when Cunningham (Scottish) Acres are used, this is usually noted.
If you’re tracing a particular piece of property, or the history of a townland, you need to be aware of the conversions to English Acres since that was the standard after the 1830s. These are as follows:
1 Irish (Plantation) Acre = 1.6 English Acre (rounded off from 1.6198 to be exact)
1 Cunningham (Scottish) Acre = 1.3 English Acre (rounded off from 1.2913 to be exact)
I first encountered the use of the Cunningham (Scottish) Acre measurement in the rent books for a large and prominent Ulster landowner. To make sense of it, I simply used the formula listed above, and I could then key the property to some degree into Griffith’s Primary Valuation which is in standard English Acres.
For your reference, while most of the world has gone to the metric system, the United States, and some Commonwealth countries still uses English Acres as its basic unit of measurement. This at least provides some visual as to what is meant by an “acre” in this discussion.
Some interesting websites for old measurements include “Index to Units & Systems of Units” www.sizes.com/units/index.php; and a wonderful article by George Gilmore of the Garvagh Historical Society (2011) “What Size is an Acre” www.billmacafee.com/valuationrecords/whatsizeisanacre.pdf is a must to consult.