Winter's Formula Calculator (Metabolic Acidosis)
Winter's formula gives the expected PaCO₂ in a simple metabolic acidosis — 1.5 × bicarbonate + 8 ± 2 mmHg — so you can check whether respiratory compensation is appropriate or a second acid–base disorder is present.
Quick answer
Winter’s formula gives the expected PaCO₂ in a simple metabolic acidosis: expected PaCO₂ = 1.5 × bicarbonate + 8 ± 2 mmHg. If the measured PaCO₂ sits within this range, respiratory compensation is appropriate; above it suggests a concurrent respiratory acidosis, and below it a concurrent respiratory alkalosis.
Winter's formula inputs
Validated formula
Expected PaCO₂ (mmHg) = 1.5 × [HCO₃⁻] + 8 ± 2. Compute the range using ±2. Used in metabolic acidosis to check whether respiratory compensation is appropriate.
Interpretation
- Measured PaCO₂ within expected range— Appropriate respiratory compensation for a simple metabolic acidosis.
- Measured PaCO₂ above expected range— Concurrent respiratory acidosis (inadequate compensation).
- Measured PaCO₂ below expected range— Concurrent respiratory alkalosis (over-compensation / additional process).
How to use the Winter's Formula calculator
- 1Enter the bicarbonate. Enter the serum bicarbonate (HCO₃⁻) in mEq/L.
- 2Optionally enter the measured PaCO₂. Enter the measured PaCO₂ if you want to check whether compensation is appropriate.
- 3Read the expected range. The tool shows the expected PaCO₂ range and, if a measured value is given, whether compensation is appropriate or a second disorder is present.
Medical disclaimer: This is general health information, not medical advice. It does not diagnose or treat any condition, and the results are estimates based on public reference formulas. Always consult a qualified doctor about your individual health. If you think you may have a medical emergency, contact your local emergency services immediately.
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Book a consultationFrequently asked questions
What is Winter’s formula used for?⌄
It checks whether the lungs are compensating appropriately for a metabolic acidosis. A measured PaCO₂ outside the expected 1.5 × HCO₃⁻ + 8 ± 2 range points to an additional respiratory acid–base disorder.
What does a PaCO₂ above the expected range mean?⌄
It suggests inadequate respiratory compensation — a concurrent respiratory acidosis on top of the metabolic acidosis. A clinician interprets this with the full arterial blood gas.
Does Winter’s formula apply to metabolic alkalosis?⌄
No. Winter’s formula is specifically for metabolic acidosis. Metabolic alkalosis uses a different compensation estimate.
Sources & validation
This calculator reproduces the published Winter's Formula score, validated for expected respiratory compensation in metabolic acidosis.
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