Abstract Introduction During paediatric resuscitation it is essential to be able to estimate the child's weight as it determines drug doses and equipment sizes. Age and length-based estimations exist, with age-based estimations being especially useful in the preparation phase and the length-based Broselow tape having weight-based drug doses and equipment already assigned via a colour code system. The aim of this study was to compare the actual recorded weights of Australian children to the predicted weights using the original and updated APLS, Luscombe and Owens and Best Guess formulae and the Broselow tape. Method A retrospective observational study of children attending an Australian tertiary children's hospital. Results From 49,565 patients extracted from the database, 37,114 children with age and weight and 37,091 children with age and height recorded were included in the analysis. Best Guess was the most accurate, with the smallest overall mean difference 0.86kg. For <1 year old, Broselow tape was the most accurate (mean difference −0.43kg), Best Guess was the most accurate for ages 1–5 years and 11–14 years (mean difference 0.27 and 0.20kg respectively), and the updated APLS formula was the most accurate for 6–10 year-old (mean difference 0.42kg). The Broselow tape was able to only classify 48.9% of children into the correct weight colour band. Conclusions For an age-based weight estimation, in infants less than one year the new APLS formula is the most accurate and over one year the Best Guess formulae should be used.