Objective To evaluate the performance of five existing age-based weight estimation formulae - the original and updated Advanced Paediatric Life Support (APLS) formulae, Luscombe formula, Best Guess formula, Chinese Age Weight Rule (CAWR) - as well as a new two-part weight estimation formula, the Chinese Age Weight Rule-3 (CAWR-3), in Hong Kong children presenting to the emergency department (ED). Methods Data based on children aged 1-12 who presented to the ED of a tertiary referral centre in Hong Kong over a six-month period. Actual weight was compared against estimated weight from the weight estimation formulae. Level of agreement was assessed by Bland-Altman analysis using mean percentage difference (MPD) and 95% limits of agreement (LOA). Root mean squared error (RMSE) and proportions of weight estimates within 10%, 15% and 20% of actual weight were calculated. Results A total of 4600 children were included. The CAWR-3 outperformed the five existing weight estimation formulae. The CAWR-3 had the least MPD in age 4-12 (MPD +3.2%), as well as the second least MPD in age 1-12 (MPD -0.7%). The CAWR-3 had narrowest 95% LOA in age 1-3 (95% LOA -32.6% to 21.9%) and the second narrowest 95% LOA in age 1-12 (95% LOA -37.5% to 36.1%). The CAWR-3 had the smallest RMSE of 6.33 kg in age 4-12 and the smallest RMSE of 4.90 kg in age 1-12. Furthermore, the CAWR-3 had the highest proportion of weight estimates within 10%, 15% and 20% of actual weight. Conclusion The CAWR-3 outperforms the five existing age-based weight estimation formulae in Hong Kong children presenting to the emergency department.