Clinical & Lifestyle
Kidney function, body surface area, and blood alcohol — measures that come from a lab report or a clinical setting rather than a gym.
Four calculators for numbers that arrive from somewhere other than a gym: a lab report, a drug label, an oncology dose sheet, a legal limit.
What they have in common is that each one is easy to compute and easy to misread. The arithmetic is the small part; what the number does and does not license is the rest of the page.
GFR Calculator
Estimate your kidney filtration rate from a blood test, using the race-free CKD-EPI 2021 equation.
Open calculatorBody Surface Area Calculator
Calculate your body surface area with eight published formulas, side by side.
Open calculatorBlood Alcohol Calculator
See how alcohol clears your system over time — an educational estimate, never a fitness-to-drive test.
Open calculatorWhich one for which question
| Question | Use | Based on |
|---|---|---|
| What does my kidney result mean? | GFR | CKD-EPI 2021, race-free |
| What is my body surface area? | Body Surface Area | Mosteller, Du Bois and six more |
| What shape are my measurements? | Body Type | FFIT circumference thresholds |
| How does alcohol clear my system? | Blood Alcohol | Widmark with Watson body water |
A number from a lab is not a diagnosis
Every equation on these pages was fitted to a population and then applied to an individual, and the gap between those two things is where the misreading happens. An eGFR of 58 is not a disease; it is one reading, on one day, from one marker that also moves with muscle mass and what you had for dinner. Chronic kidney disease requires the change to persist for three months, and usually a second marker alongside it.
None of these replace a clinician
These calculators reproduce published equations so you can understand a result you have already been given. They cannot examine you, they do not know your history or your medications, and they should never be the reason you start, stop or change a treatment.
Why the race coefficient is gone
Until recently, eGFR equations applied a multiplier that raised the reported figure for Black patients — an artefact of population averages in the original cohorts, treated as biology. In practice it made kidney function look better than it was, delaying referral, specialist care and transplant waitlisting.
In 2021 a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended a refit equation with race removed entirely. That is the equation used here, and there is no race input on the page.
Frequently asked questions
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