National Physical Laboratory

How can I determine my local values of gravitational acceleration and altitude? (FAQ - Pressure)

To calculate a pressure value using a liquid column - for example a mercury barometer - or a pressure balance it is necessary to know the gravitational acceleration at the location of the instrument. It can be determined by measurement on site, calculation or interpolation of measured values.

The variation in the value of g across the earth's surface is about 0.5 % due to latitude, plus a change of approximately 0.003 % per 100 m altitude. Local topography and tidal forces also can have small effects.

An approximate value for g, at a given latitude and height above sea level, may be calculated from the formula:

g = 9.780 327 (1 + A sin2 L - B sin2 2L) - 3.086 × 10-6 H m·s-2


A = 0.005 302 4
B = 0.000 005 8
L = latitude
H = height in metres above sea level

The uncertainty in the value of g so obtained is generally less than ±5 parts in 105.

Alternatively, the local value of g in the UK may be found from the data which has been gathered by the British Geological Survey (BGS) national gravity survey. BGS has made measurements of g throughout the UK and will advise on the nearest survey station. Small corrections for height and latitude differences are then applied to find the acceleration due to gravity at the point required. Gravitational data can also be obtained from BGI in France.

Ordnance Survey provide reference point bench marks of height above sea level across the UK.

Last Updated: 7 Mar 2016
Created: 9 Aug 2007


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