Objective To determine the accuracy with which parents can estimate preschool children's weight using home scales in order to calculate antipyretic dose.

Design Cross-sectional, method comparison study.

Setting and participants 156 preschool children aged 6 months to 6 years recruited from primary care and the community to an antipyretic strategies trial and managed at home.

Comparison and outcome measures Research nurse weight estimate using Seca 835-2 digital paediatric scales compared with parental weight estimate using usual home scales.

Results Parents of 62 (40%) preschool children had home scales. Research scale estimated weights were heavier than home scale weight estimates, with a mean difference of 0.41 kg (95% CI −0.24 to 0.74 kg), with 95% limits of agreement of −2.44 to 1.47 kg.

Conclusion Weight can be estimated accurately enough to calculate antipyretic medicine doses by the minority of parents having scales that can be used to estimate their child's weight.