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Find sources: "Irish units of measurement" – news · newspapers · books · scholar · JSTOR (June 2009) (Learn how and when to remove this message) |
Inold Irish law, a wide variety of measurements were used.
Atroighid ("foot") was the length of a man's foot, divided into twelve ordlach, "thumb-lengths". These figures assume a man's foot to measure 25 cm (10 inches).
| Table of length units | |||||
|---|---|---|---|---|---|
| Unit | Meaning | Relative value |
SI value |
Imperial value |
Notes |
| grain | grain | 1/36 | 0.7 cm | 1/4 inch | |
| ordlach | thumb-length | 1/12 | 2.1 cm | 0.8 in | |
| bas | palm | 1/3 | 8.4 cm | 3.3 in | |
| dorn | fist | 5/12 or 1/2 | 10.4 or 12.5 cm | 4 or 5 in | |
| troighid | foot | 1 | 25 cm | 9.9 in | |
| céim | step | 2.5 | 62.5 cm | 2 ft 1 in | |
| deiscéim | double-step | 6 | 1.5 m | 4 ft 11 in | |
| fertach | rod | 12 | 3 m | 9 ft 10 in | |
| forrach | 144 | 36 m | 39.4 yards | ||
Amagh-space was a unit set at the distance from which a cock-crow or bell could be heard. Other units such as inntrit and lait appear in documents; their value is uncertain, perhaps being equivalent to 1 and 2 fertachs respectively.
The basic unit of area was the tir-cumaile, "land of three cows", as it was an area of land that was at some point worth three cows. It is sometimes erroneously interpreted as the area needed to graze three cows, but it is far too large for that; in modern Ireland, a cow grazes on about 0.4 ha, so twenty or more could graze a tir-cumaile. Ireland in total covered about 870,000 tir-cumaile.
| Table of area units | |||||
|---|---|---|---|---|---|
| Unit | Meaning | Relative value |
SI value |
Imperial value |
Notes |
| tir-cumaile | land of three cows | n/a | 9.3 ha | 23 ac | 72 square forraigh |
| achar | acre | 1 | Adopted following Norman invasions. | ||
| seisrech | plough-land | 120 | |||
| baile | townland | 1,440 | The term "townland" is still used to designate very small named areas in the countryside. | ||
| tuath | 4,320 | Originally a term for a petty kingdom. | |||
Ahen's eggshell was used as a standard unit, roughly 55 ml.
| Table of capacity units | |||||
|---|---|---|---|---|---|
| Unit | Meaning | Relative value |
SI value |
Imperial value |
Notes |
| eggshell | 1 | 55 ml | 2 fl. oz. | ||
| méisrin | 12 | 660 ml | 1 pint 3 fl. oz. | ||
| Table of mass units | |||||
|---|---|---|---|---|---|
| Unit | Meaning | Relative value |
SI value |
Imperial value |
Notes |
| grain | 1/8 | 0.05 g | 0.772 Gr | One grain of the best wheat. | |
| pinginn | penny | 1 | 0.4 g | 6.173 Gr | |
| screpall | scruple | 3 | 1.2 g | 18.519 Gr | |
| unga | ounce | 72 | 28 g | 1 oz | Word borrowed from the Latin uncia, although an older native name was mann. |
Anight (oídhche) was used as a measure for time, in preference to a day. Unlike most traditional societies, the Irish held that a new day began at sunset, not at sunrise, so that a Wednesday night would precede the day of Wednesday.
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