Specific gravity (often abbreviated “Spec Grav” or “SG”) on a urinalysis (UA) report measures how concentrated your urine is. It compares the weight of your urine to the weight of pure water, which has a specific gravity of 1.000. The normal range for adults is 1.005 to 1.030. A higher number means more dissolved substances in your urine, while a lower number means it’s more dilute.
What the Number Actually Tells You
Your kidneys constantly adjust how much water they retain or release to keep your body’s fluid balance stable. Specific gravity reflects how well they’re doing that job. When your body needs to conserve water, your kidneys produce smaller amounts of concentrated urine, pushing the specific gravity higher. When you have plenty of fluid, they flush out the excess, and the specific gravity drops closer to that of water.
The dissolved substances being measured include electrolytes, waste products like urea, and other compounds your body is filtering out. Because specific gravity captures all of these together in a single number, it gives a quick snapshot of kidney concentrating ability without needing more complex lab tests.
Normal Ranges by Age
For anyone over one year old, the normal range is 1.001 to 1.030. Infants under one year have a narrower range of 1.002 to 1.006, because their kidneys are still maturing and can’t concentrate urine as effectively as adult kidneys.
Your specific gravity naturally fluctuates throughout the day. A morning sample is typically more concentrated (higher number) because you haven’t been drinking water overnight. A sample taken after drinking several glasses of water may fall toward the lower end. A single reading outside the normal range doesn’t necessarily signal a problem.
What a High Reading Means
A specific gravity above 1.030 suggests your urine is unusually concentrated. The most common and benign cause is simple dehydration: you haven’t been drinking enough fluids, so your kidneys are holding onto water. Vomiting, diarrhea, heavy sweating, or fever can all push the number up by reducing your body’s water supply.
Certain substances dissolved in urine can also raise the reading. Glucose spilling into urine (as happens with uncontrolled diabetes) increases specific gravity. For every gram of glucose per deciliter of urine, specific gravity rises by roughly 0.003 to 0.005. Contrast dye used in imaging scans can temporarily elevate the number as well. Your doctor will consider these possibilities when interpreting the result.
Less commonly, conditions that cause the body to inappropriately retain water, leading to very concentrated urine, can push specific gravity higher. Heart failure and certain hormonal imbalances fall into this category.
What a Low Reading Means
A specific gravity below 1.005 means your urine is very dilute. Again, the simplest explanation is that you drank a lot of water before the test, and your kidneys are doing exactly what they should: flushing out the surplus.
When a low reading persists and can’t be explained by fluid intake, it may point to conditions where the kidneys lose their ability to concentrate urine. Diabetes insipidus (a hormonal condition unrelated to blood sugar) is one example. In this condition, the body either doesn’t produce enough of the hormone that tells the kidneys to retain water, or the kidneys don’t respond to it properly. Kidney infections, high blood calcium, low potassium, and liver failure can also impair the kidneys’ concentrating ability.
Why a Fixed Reading at 1.010 Matters
If your specific gravity stays locked around 1.010 regardless of how much you drink, that’s a finding called isosthenuria. At 1.010, urine has roughly the same concentration as blood plasma before it gets filtered. This means your kidneys are neither concentrating nor diluting the urine. They’re essentially letting fluid pass through without adjusting it.
A fixed reading at 1.010 can be an early sign that the kidneys have lost significant filtering capacity, as seen in chronic kidney disease. Healthy kidneys should be able to swing the specific gravity up when you’re dehydrated and down when you’re well-hydrated. When they can’t do either, it suggests the tiny tubules responsible for fine-tuning urine concentration are damaged.
How It’s Measured
Two common methods are used. The first is the urine dipstick, a chemically treated strip dipped into the sample. It’s fast, inexpensive, and included in every standard urinalysis. The second is a refractometer, an instrument that measures how light bends as it passes through the urine. Refractometry is generally considered more precise and less affected by interfering substances like protein or blood pigments in the sample.
Specific gravity is sometimes compared to a more detailed measurement called urine osmolality, which counts the actual number of dissolved particles. Osmolality is more exact, but specific gravity remains widely used because it’s quick, cheap, and available on a standard dipstick. For most clinical purposes, specific gravity provides enough information. It’s also useful for self-monitoring: people who form kidney stones, for example, benefit from checking that their urine stays dilute, and specific gravity is the easiest way to track that at home.
What to Make of Your Result
If your UA report shows a specific gravity between 1.005 and 1.030, the result is normal. A value slightly outside that range on a single test usually reflects how much you happened to drink that day rather than a kidney problem. The result becomes more meaningful when it’s consistently abnormal across multiple tests, when it’s paired with other abnormal findings on the urinalysis (like protein or blood), or when it stays fixed at 1.010 despite changes in fluid intake.
Specific gravity is one piece of a larger picture. On its own, it’s a rough gauge of hydration and kidney concentrating power. Combined with the rest of your urinalysis results and your symptoms, it helps clarify whether your kidneys are filtering and adjusting fluid the way they should be.