Category: Misc.

The rai is a unit of land measurement here in Thailand. You’ll see references to land the size of so-and-so rai, etc. But exactly how much area, I was wondering yesterday, is one rai?

In researching the answer to that question, I stumbled upon this:

rai: a traditional unit of land area in Thailand. The rai is now considered to equal exactly 1600 square meters, which is 0.16 hectare or approximately 0.3954 acre. The rai is divided into 4 ngan. The unit is called the hai in northern Thailand and the lai in Laos. The word means “field,” that is, an upland field rather than a rice paddy.

The rest of the site — How Many? A Dictionary of Units of Measurement — is really worth checking out. It’s maintained by a guy named Russ Rowlett, who’s a math prof at UNC-Chapel Hill.

I especially like this:

What countries besides the U.S. have not adopted the metric system?
Many U.S. teachers think the answer is “Liberia and Burma” (make that Myanmar). Let’s give Liberia and Myanmar a break! All countries have adopted the metric system, including the U.S., and most countries (but not the U.S.) have taken steps to eliminate most uses of traditional measurements. However, in nearly all countries people still use traditional units sometimes, at least in colloquial expressions. Becoming metric is not a one-time event that has either happened or not. It is a process that happens over time. Every country is somewhere in this process of going metric, some much further along than others.

And:

Americans probably use a greater variety of units of measurement than anyone else in the world. Caught in a slow-moving transition from customary to metric units, we employ a fascinating and sometimes frustrating mixture of units in talking about the same things. We measure the length of a race in meters, but the length of the long jump event in feet and inches. We speak of an engine’s power in horsepower and its displacement in liters. In the same dispatch, we describe a hurricane’s wind speed in knots and its central pressure in millibars.

Furthermore, our English customary units do not form a consistent system. Reflecting their diverse roots in Celtic, Roman, Saxon, and Norse cultures, they are often confusing and contradictory. There are two systems for land measurement (one based on the yard and the other on the rod) and a third system for distances at sea. There are two systems (avoirdupois and troy) for small weights and two more (based on the long and short tons) for large weights. Americans use two systems for volumes (one for dry commodities and one for liquids) and the British use a third (British Imperial Measure).

Some other interesting units of land measurement include: the tatami (yes, like the mat — thanks for the heads up, Mech and K!), the olk, and the soendre.