つぼりょう, べいつぼ, めーとるつぼりょう【坪量, 米坪, メートル坪量】
■ The weight of paper in grams per one square-metre sheet of paper, expressed in units of g/m2 or gsm (grams per square metre) and used to indicate the thickness of the paper.
□ The term 坪量 derives from the fact that the measurement was traditionally based on a piece of paper cut to 1尺 x 1尺, where 1尺（しゃく） = approx. 30.3 cm. Although 坪 is commonly a 6尺 x 6尺 square unit used to measure land area, it can also mean a 1尺 x 1尺 square, also referred to as 尺坪（しゃくつぼ）.
Today 坪量 is synonymous to メートル坪量, or 米坪 for short, which is a metric version of 坪量 and is the same as the grammage or "gsm" weight used in countries that have adopted the metric system (that is, nearly all countries except the United States).
Although 坪量 is often translated as "basis weight", this can be confusing. In the US, the basis weight of paper is not the grammage but the weight in pounds of one ream (500 sheets) of paper cut to the basic size for its grade.
See this page for US basis weight and grammage conversion tables.
See also 連量.
This entry was created by Yuno Hanlon.