What this calculator does
Winters’ formula (expected pCO₂) works out checks whether respiratory compensation for a metabolic acidosis looks appropriate. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaExpected pCO2 = 1.5 × HCO3 + 8, ± 2 mmHg
The inputs explained
| Field | What to enter |
|---|---|
| Bicarbonate (HCO3) (mEq/L) | A number, measured in mEq/L. Starts at 14. |
| Measured pCO2 (0 if unknown) (mmHg) | A number, measured in mmHg. Starts at 0. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with bicarbonate (hco3)
Every other input is held at the calculator’s starting values while bicarbonate (hco3) varies. Select any row to load that scenario into the calculator.
How the answer changes with bicarbonate (hco3)
| Bicarbonate (HCO3) (mEq/L) | Expected pCO2 | Expected range | Note |
|---|---|---|---|
| 7 | 18.5 mmHg | 16.5 - 20.5 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |
| 10.5 | 23.8 mmHg | 21.8 - 25.8 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |
| 14 | 29.0 mmHg | 27.0 - 31.0 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |
| 21 | 39.5 mmHg | 37.5 - 41.5 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |
| 28 | 50.0 mmHg | 48.0 - 52.0 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |
| 42 | 71.0 mmHg | 69.0 - 73.0 mmHg | Only valid for a primary metabolic acidosis, and only within the usual clinical bicarbonate range. |