In metabolic acidosis the lungs compensate by breathing faster to blow off carbon dioxide. If the measured PaCO₂ is higher than predicted, there is also a respiratory acidosis; if lower, a respiratory alkalosis.
How to use the Winters’ Formula Calculator
- Bicarbonate
- Measured PaCO₂ (optional)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter bicarbonate and, optionally, the measured PaCO₂.
Inputs explained
| Field | What to enter |
|---|---|
| Bicarbonate | In mEq/L |
| Measured PaCO₂ (optional) | In mmHg |
What each result means
- Expected PaCO₂ = 1.5×[Bicarbonate] + 8
- Expected range from = [Expected PaCO₂] – 2
- Expected range to = [Expected PaCO₂] + 2
Example values
How the main result changes when Bicarbonate changes and everything else stays at the example values above:
| Bicarbonate (mEq/L) | Expected PaCO₂ (mmHg) |
|---|---|
| 6 | 17 |
| 9 | 21.5 |
| 12 | 26 |
| 15 | 30.5 |
| 18 | 35 |
| 24 | 44 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Expected PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2 mmHg
Worked example
Inputs — Bicarbonate: 12 mEq/L; Measured PaCO₂ (optional): 26 mmHg.
Results — Expected PaCO₂ = 26 mmHg; Expected range from = 24 mmHg; Expected range to = 28 mmHg; Measured vs expected = Appropriate compensation.
Key terms
- PaCO₂
- Partial pressure of carbon dioxide in arterial blood.
Frequently asked questions
When is Winters' formula used?
Only in metabolic acidosis.
What is a quick check?
Expected PaCO₂ roughly equals the last two digits of the pH (e.g. pH 7.25 → about 25 mmHg).
How quickly does compensation happen?
Within 12–24 hours.