<P> A useful convention for normal laboratory work is to quote molar masses to two decimal places for all calculations . This is more accurate than is usually required, but avoids rounding errors during calculations . When the molar mass is greater than 1000 g / mol, it is rarely appropriate to use more than one decimal place . These conventions are followed in most tabulated values of molar masses . </P> <P> Molar masses are almost never measured directly . They may be calculated from standard atomic masses, and are often listed in chemical catalogues and on safety data sheets (SDS). Molar masses typically vary between: </P> <Dl> <Dd> 1--238 g / mol for atoms of naturally occurring elements; </Dd> <Dd> 10--1000 g / mol for simple chemical compounds; </Dd> <Dd> 1000--5,000,000 g / mol for polymers, proteins, DNA fragments, etc . </Dd> </Dl> <Dd> 1--238 g / mol for atoms of naturally occurring elements; </Dd>

How do you determine the molar mass of a substance