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.
Important! Your births data will be held and processed locally in your browser. No data will be sent to our server.
There is nothing to import. Paste some data into the Births box and try again.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.
The CSV file format is supported by almost all spreadsheets and database management systems, including Microsoft Excel, Apple Numbers, LibreOffice Calc and Apache OpenOffice Calc.
Your data must contain the following variables:
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, BirthWeight
1, 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
Important! These records were not imported because they contain values that are invalid or outside the calculator's range. Consequently, they are exluded from the charts, tables and totals shown in this tool.
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.
These settings will be stored in your browser.
The totals for actual births and expected births might not correspond owing to rounding errors.Save your birth weight centile data for use in analysis software and spreadsheets such as SPSS and Microsoft Excel.
Save birth weight centilesThe calculator exports data in the comma-separated values (CSV) file format.
Exported data includes the following variables:
* Values depend on current category boundaries settings; see corresponding category label variable for definition
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.
The term centile is short for percentile. If a baby's birth weight is on the 50th centile, then half of babies (50%) born at the same gestational age in the population have a lower birth weight. If a baby's birth weight is on the 3rd centile it means that three out of 100 babies (3%) born at the same gestational age will have a lower birth weight than them.
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.
This calculator is 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.
If you have a suggestion, or you experience a technical issue, please send feedback to help us improve this resource.
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