Clinical Medicine & Physiology
Weir Equation Indirect Calorimetry Calculator: Resting Energy Expenditure (REE) & RQ
Calculate gold-standard Resting Energy Expenditure REE (kcal/day) = 1.44 * (3.941 * VO2 + 1.106 * VCO2) (and urinary-nitrogen complete Weir REE) plus Respiratory Quotient RQ = VCO2 / VO2 from metabolic cart gas exchange.
Why J. B. de V. Weir’s 1949 stoichiometry remains the ICU and exercise-lab gold standard!
Predictive calorie equations can miss an ICU or burn patient’s actual metabolic rate by +-500 kcal/day! J. B. de V. Weir (1949, J. Physiol.) solved exact carbohydrate/fat/protein oxidation stoichiometry to derive Resting Energy Expenditure from minute oxygen consumption VO2 (mL/min STPD) and carbon dioxide production VCO2 (mL/min STPD): Complete Weir REE (kcal/day) = 1.44 * (3.941 * VO2 + 1.106 * VCO2) - 2.17 * UUN_g_day, where 1.44 converts L/min (1/1000) across 1,440 minutes/day!
Weir simultaneously proved that omitting urinary urea nitrogen (Abbreviated Weir: 1.44 * (3.941 * VO2 + 1.106 * VCO2)) introduces < 1%–2% error across physiologic protein oxidation shares! Pairing REE with Respiratory Quotient RQ = VCO2 / VO2 checks test validity immediately (physiologic range ~0.67 ketosis/fat to ~1.00 pure carbohydrate up to ~1.25 lipogenesis/overfeeding; values outside 0.67–1.30 flag cuff leaks or hyperventilation!).
| Respiratory Quotient RQ = VCO2 / VO2 | Predominant Substrate / Metabolic State |
|---|---|
| RQ ~ 0.70 (0.67–0.73) | Predominant lipid / ketone oxidation (fasting or ketogenic state) |
| RQ ~ 0.82–0.85 | Balanced mixed macronutrient oxidation |
| RQ ~ 1.00 | Pure carbohydrate oxidation |
| RQ > 1.00 (1.01–1.25) | Net de novo lipogenesis (overfeeding) or acute hyperventilation CO2 washout |
Abbreviated & Nitrogen-Corrected Weir Resting Energy Expenditure REE (kcal/day)
Evaluates 1.44 * (3.941 * VO2 + 1.106 * VCO2) - 2.17 * UUN for VO2 (mL/min in B2), VCO2 (mL/min in B3), and 24-hour urinary urea nitrogen UUN (g/day in B4; enter 0 for standard Abbreviated Weir) within physiologic RQ 0.65..1.35.
=IF(OR(B2 <= 0, B3 <= 0, B4 < 0, B3 / B2 < 0.65, B3 / B2 > 1.35), "Non-Physiologic Gas Exchange or Leak (Check RQ 0.65–1.35)", ROUND(1.44 * (3.941 * B2 + 1.106 * B3) - 2.17 * B4, 1))Metabolic Cart Respiratory Quotient RQ = VCO2 / VO2
Computes ROUND(B3 / B2, 3) to audit circuit integrity and substrate utilization.
=IF(OR(B2 <= 0, B3 <= 0), "Requires Positive VO2 and VCO2", ROUND(B3 / B2, 3))Try the example
Use the original values or change them to test your understanding.