What is the numerical value of the speed of light?

At present, the numerical value of the gravitational constant G cannot be determined experimentally to better than about 1 part in 7000. The resulting uncertainty in G (in SI, cgs, or similar systems of units) is far greater than that of any of the four other fundamental empirical constants. This uncertainty carries over to all Planck units that depend on G. By contrast, the speed of light in SI units is no longer subject to measurement error, because the SI unit of length, the metre, is now defined as some chosen fraction of the distance light travels in 1 second. Hence the speed of light is an exact defined quantity.