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Kidney Function (BUN/Creatinine) Calculator

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Enter your BUN and creatinine results to check each value and your BUN/Creatinine ratio.

Kidney Function Calculator

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BUNNormal
CreatinineNormal
BUN/Creatinine ratio15.6 (Normal)
This is informational only, not a diagnosis. Kidney function is best assessed alongside eGFR and clinical context - discuss results with a doctor.

The reference ranges

BUN: under 7 Low, 7-20 mg/dL Normal, over 20 High Creatinine: Men 0.6-1.2 mg/dL Normal, Women 0.5-1.1 mg/dL Normal BUN/Creatinine ratio = BUN / Creatinine Under 10: Low - 10 to 20: Normal - Over 20: High
Example

BUN 22 mg/dL, Creatinine 0.8 mg/dL: ratio = 22/0.8 = 27.5, in the High range - creatinine alone stays comfortably Normal while BUN and the ratio both climb, a pattern more consistent with dehydration than with reduced kidney filtering.

Step-by-step guide

  1. Get a basic or comprehensive metabolic panel from a blood test - BUN and creatinine are standard components.
  2. Enter both values in mg/dL along with your sex, since the creatinine range differs between men and women.
  3. Review each value plus the ratio - the ratio can reveal patterns like dehydration that the individual numbers alone might not.

What the ratio adds beyond the individual values

BUN and creatinine are both waste products filtered by the kidneys, but they respond differently to non-kidney factors: BUN rises with dehydration, high protein intake, or GI bleeding, while creatinine (produced by muscle breakdown) stays relatively stable regardless of diet or hydration. When both rise together, it usually points toward reduced kidney filtering. But when the ratio climbs while creatinine stays normal, it's more often a sign of dehydration or another non-kidney cause - a distinction the ratio makes visible that looking at either value alone would miss.

Common mistakes

Assuming a high BUN alone means kidney disease - a high BUN with normal creatinine is more often explained by dehydration, a high-protein diet, or GI bleeding than by kidney damage.
Not accounting for muscle mass when interpreting creatinine - very muscular individuals naturally produce more creatinine, which can push a healthy person's result toward the upper end of normal or slightly above.

Frequently asked questions

What does a high BUN/Creatinine ratio usually mean?

The most common cause is dehydration. If both BUN and creatinine are individually normal but the ratio is elevated, adequate hydration and a repeat test is usually the first step, rather than an immediate concern about kidney disease.

What does a low BUN/Creatinine ratio mean?

It's less common, and can be associated with very low protein intake (as in malnutrition), liver disease, or conditions with reduced muscle mass affecting creatinine production.

Is this the same as an eGFR test?

No - eGFR (estimated glomerular filtration rate) is a separate, more comprehensive calculation that factors in creatinine along with age and sex to estimate overall kidney filtering capacity. BUN and creatinine on their own are useful screening markers, but eGFR gives a more complete picture.

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