Free Water Clearance Calculator

Calculate free water clearance to assess renal water handling and dilution ability.

Aug 31, 2026 Renal #free-water-clearance #water-balance #osmolality

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All fields required unless noted

Urine osmolality (mOsm/kg)

Serum osmolality (mOsm/kg)

Urine flow rate (mL/min)

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Enter your values and press Calculate to see the result.

Formula & Clinical Notes

Formula

CH₂O = V × (1 − UOsm / SOsm)

Clinical Notes

Free water clearance (CH₂O) is the difference between urine flow and osmolar clearance. A positive value indicates net free water loss (dilute urine) and a negative value (often reported as tubular water reabsorption) indicates net water retention (concentrated urine). It is used to evaluate disorders of water balance.

Sources

StatPearls — Serum Osmolality