纸张定量又叫克重，在香港和台湾则称为基重，常用公制gsm表示，这是国际通用符号。

　　但是美国和英国却採用英制，用磅（Lb）计量纸重，并以点（Point）表示纸和纸板的厚度，以及作為划分纸和纸板的标尺，规定12个点以上者為纸板；12个点以下者為纸张。1点就是千分之一英寸，若换算為公制：1点=0.0254mm；12点≈0.3mm。由此可知，0.3mm厚度是纸和纸板的分界线。

　　在美国纸板的定量(牛卡和牛皮纸)还有另外两种表示法（习惯用法）：磅/1000英尺2（LBS/1000ft2）和磅/3000英尺2（LBS/1000ft2），前者用於厚纸板；后者用於薄纸板。

　　如果由英制换算为公制，乘以系数就可以了：克/米2=（磅/1000英尺2）×4.888；克/米2=（磅/3000英尺2）×1.627

　　我们常用的单位正确的说是GSM（GramSquareMeter）也就是ｇ／㎡，这是以单张纸来计算的。

　　磅数和GSM的换算法：

　　磅数＝克数×英吋数（纸长宽换算成英制）／1406

Weight

1 gram =0.002204 pounds(lb.) 1 mt =2.204 lbs.

1 meter 39.3696 inches 1 sm =1549 sqin

Gsm = gram per square meter

= 0.002204 lb/1549 sqin = 0.0000014228 lb/sqin

weight of 1 ream of paper (500 sheets)

Formula commonly used:gsm x 0.0007114 x width(inches) x Lenght(inches)/2204

Example : the weight of 1 ream 130 gsm 35" x 47" paper

=130 x 0.0007114 x 35 x 47/2204 = 0.06902 mertic tonne

Thickness

Micron : 1 micron = 0.001 mm

Point : 1 Point = 0.001 inch

Thickness of 1 ream of paper (500 sheets)

in mm = micron x 500/1000 or (point x 500/1000) x 25.4

in inches = point x 500/1000 or (micron x 500/1000)/25.4

Sheets per inch =1/(point / 1000)

PPI = number of pages per inch = 2 x number of sheets per inch = 2/(point/1000)

Thickness converting table for um(微米) to PPI

um(微米) - PPI厚度对换表

Price

HK$/gsm :Unit ream price per gsm for standard paper size 31" x 43",Prices for other sheet sizes to be in proportin to 31" x 43"

Example : 130 gsm 35" x 47" @HK$2.90/gsm

HK$2.90 x 130 = HK$377.00 per ream in 31" x 43"

For 35"x47" = HK$377.00 x (35x47)/(31x43) = HK$465.24/ream

HK$/tonne : Unit metric tonne price can be obtained by HK$/gsm x 2325.(2325 is the conversion factor adapted by HTH.)

Example :HK$2.90 x 2325 HK$6742.50 per metric tonne