Conversion of radio carbon dates

When dealing with radio carbon dates, one has to remember that the measured date is not the calendar date. For this one has to calibrate the radio carbon date Uncal BP (in former times written as bp or as bc [=Uncal BP-1950]) towards the calendar date BP or BCE  (in former times written as Calbc).
The following table is calculated with the help of the program CALIB (using data from Stuiver, M. and Pearson, 1993).
The uncertainty in the radio carbon date Uncal BP is taken 100 years. The error/uncertainly in the calendar date (Cal) BCE is then in the order of 80 years (1 sigma).
Conversion table
Period Radio carbon date Avg. Calendar date

Uncal BP (Cal)BCE
middle bronze 2950 1140
middle bronze 3450 1780
early bronze 3550 1860
early bronze 3730 2220
late neolithic 3950 2430
late neolithic 4450 3170
early neolithic 4950 3720
early neolithic 5450 4290

Remember that in practice this is not a straight line,
it has many dips in it, but it gives a general indication at least.

A CALIB computer program (Windows) and a web page are available to calculate the conversion.

Conversion historical dates and astronomical dates

Historical Date
Astronomical Date
2 CE
1 CE

Another thing to remember when looking at astronomical dates, is that most computer programs use the Julian calendar before October 15th, 1582  (even in the BCE times, while we don't know the calendaring then) instead of the Gregorian calendar we use at present dates. So e.g. December 21st, 2800 BCE becomes January 11th, -2798.

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Last content related changes: August 29, 1997