What Does Specific Gravity Mean on a Urine Test?

What it means

Specific gravity compares how heavy a liquid is with the same amount of pure water. Urine contains dissolved salts, waste and other substances, so it is a little heavier than water. The more concentrated the urine, the higher the number.

It is one line of a standard urinalysis, measured by a dipstick or a machine. Your kidneys change how concentrated urine is all day long, depending on how much you drink, sweat and eat. A higher reading suggests concentrated urine, and a lower one suggests dilute urine. Doctors also use it to judge how much to trust other lines on the report, because very dilute urine can make other substances look lower than they really are.

Specific gravity is related to, but not the same as, osmolality, a more exact lab measure of dissolved particles. It does not measure protein, sugar or infection on its own; those have their own lines on the urine report.

Where you may see it

• The 'Physical' or 'Chemistry' section of a urinalysis report
• Urine dipstick results recorded in clinic or hospital notes
• Pre-employment or routine health check urine results