Use this calculator to derive the birth weight centiles for groups of singleton babies born between 24 and 42 completed weeks of gestation.
Paste your birth data in the Births box below and then click Import births. For demo purposes, you may use our sample data. For help and information about birth weight centiles, see the Help tab.
About the import file format
The calculator supports two commonly used text file formats: delimited text files, in which the TAB character typically separates each field of text, and comma separated values text files (.csv), in which the comma character (,) separates each field of text.
Your data must contain the following variables:
- Sex [1=boy; 2=girl]
- Gestation [24 to 42 completed weeks]
- BirthWeight [200 to 9000 grams]
Note that birth weight centiles are based on completed weeks of gestation because national birth data is only available in this format. For example, births from 32+0 to 32+6 count as 32 completed weeks.
If your data has headers, the header names must match the variable names above (names are case insensitive); if there are no headers, variables must be in the stated order. For example:
Sex, Gestation, BirthWeight1, 37, 3940
2, 27, 960
1, 33, 1700
1, 37, 3300
2, 40, 2890
2, 31, 580
1, 24, 710
2, 40, 3300
2, 40, 4100
1, 37, 4580
Here we present your births by birth weight centile, along with the centile distributions for the variables sex, gestation and birth weight. We also show (in a lighter shade) the expected number of births for each centile category, based on all births in the UK.
You can see tabulations of the charts' underlying data on the Tables tab and export your birth weight centile data from the Export tab.
Use the Settings panel to customise the category boundaries or to change how your data is presented.
Settings
These settings will be stored in your browser.
Save your birth weight centile data for use in analysis software and spreadsheets such as SPSS and Microsoft Excel.
About the export file format
The calculator exports data in the comma-separated values (CSV) file format.
Exported data includes the following variables:
- sex [1=boy; 2=girl]
- gestation [completed weeks]
- birthWeight [grams]
- centile [grams]
- centileCategory [integer*]
- sexCategory [integer]
- gestationCategory [integer*]
- birthWeightCategory [integer*]
- centileCategoryLabel [text]
- sexCategoryLabel [text]
- gestationCategoryLabel [text]
- birthWeightCategoryLabel [text]
* Values depend on current category boundaries settings; see corresponding category label variable for definition
About birth weight centiles
These birth weight centile charts offer a means of comparing the birth weight of a baby (or groups of babies) with the birth weights of 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. Our 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 also offer an individuals calculator to derive the centile or birth weight for an individual singleton baby.