Birth weight centiles calculators

Birth weight centile charts offer a means of comparing the weight of a baby (or groups of babies) at birth to babies born at the same gestational age in the UK. When assessing the birth weight of an individual baby it is hard to tell whether their birth weight is in the normal range for their gestational age and sex. Comparing their birth weight with the birth weight of a large population of babies born in the UK can be helpful for identifying those who are outside the normal range and may require monitoring.

Birth weight differs for boys and girls and by gestational age at birth and so the centiles are calculated separately for each sex and gestation in completed weeks. These centile charts are based on singleton babies who were alive at the onset of labour. They should be used with caution when assessing the birth weight centile for a baby from a multiple pregnancy or an antepartum stillbirth as these babies are likely to have a lower birth weight than singleton babies alive at onset of labour.

We offer two separate calculators: an individuals calculator to derive the birth weight or centile for an individual baby, and a batch calculator to derive and explore birth weight centiles for groups of babies.

Our calculators are based on the research paper Updated birth weight centiles for England and Wales, which used data from MBRRACE-UK for all singleton babies alive at onset of labour born in the UK between 1 February 2013 and 31 December 2014.