Derive a centile

Select the Centile option if you want to know the centile for a specific birth weight of a baby. Enter the baby's sex, gestational age (in completed weeks), and birth weight (in grams). The calculator displays the derived centile in the Centile box.

Interpret the result — say a baby's birth weight is on the 3rd centile. This means that three out of 100 babies (3%) born in the UK at the same gestational age and sex will have a lower birth weight than them. Likewise, if a baby's birth weight is on the 50th centile, then half of babies (50%) at the same gestational age and sex have a lower birth weight.

If you want to calculate and explore centiles for groups of babies, please use our batch birth weight centiles calculator.

Derive a birth weight

Select the Birth weight option if you want to know the birth weight associated with a specific centile. Enter the baby's sex, gestational age (in completed weeks), and the centile. The calculator displays the derived birth weight in the Birth weight box.

Interpret the result — for example, the birth weight associated with the 3rd centile for boys at 38 weeks' gestation is 2445g. This means that 3 in 100 baby boys born at 38 weeks' gestational age will weigh less than 2445g.