Assessing the Accuracy of Common Pediatric Age-Based Weight Estimation Formulae

Ackwerh, Ray MD, FRCA; Lehrian, Laura DO; Nafiu, Olubukola O. MD, FRCA

Anesthesia & Analgesia:
doi: 10.1213/ANE.0000000000000163
Pediatric Anesthesiology: Research Report

BACKGROUND: Many of the common equations for weight estimation in children were either introduced before the widespread prevalence of childhood obesity or have not been assessed in overweight/obese children. Therefore, we assessed the accuracy of 3 common age-based weight estimation formulae (Advanced Pediatric Life Support, Luscombe, and Theron) for predicting the weight of children undergoing elective, noncardiac operations. We also developed and validated a new age-based weight estimation formula.

METHODS: We used preoperative anthropometric and clinical data on 13,933 children aged 2 to 12 years to evaluate the performance of 3 pediatric age-based weight estimation formulae. Ability of the formulae to predict measured weights was assessed in a derivation cohort (75% randomly selected from the study sample). We also developed and validated a new age-based formula (the Michigan formula) that could be used to estimate the weight of contemporary American children.

RESULTS: Among the 10,488 children in the derivation cohort, 31.8% were overweight or obese while 55.7% were boys. The accuracy of the formulae varied considerably. The Luscombe formula demonstrated the lowest mean bias of 3.4 kg (95% confidence interval, 3.2–3.5 kg) and 89.7% of estimates within 10% of measured weight. Our derived linear regression equation the “Michigan Formula” demonstrated the highest accuracy compared with the existing formulae with a bias of 4.6 kg (95% confidence interval, = 4.36–4.84 kg) and 92% of estimates within 10% of measured weights.

CONCLUSIONS: Accuracies of current weight estimation formulae varied greatly. Our derived equation (Michigan formula: weight (kg) = 3 x age (yr) + 10) demonstrated high accuracy when compared with existing formulae and may be more applicable for estimating the weight of contemporary American children.

Author Information

From the Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan.

Accepted for publication December 6, 2013.

Funding: None.

The authors declare no conflicts of interest.

Abstract presented at the Winter Meeting of the Society for Pediatric Anesthesia, March 14–17, 2013, Las Vegas, Nevada.

Address correspondence and reprint requests to Olubukola O. Nafiu, MD, FRCA, 1500 East Medical Centre Drive, University of Michigan Health System, Room UH 1H247, Ann Arbor, MI 48109. Address e-mail to

© 2014 International Anesthesia Research Society