In order to measure this we first have to make some assumptions about the average penis size, the average duration and the average speed. So let's start the calculation. Medical studies have shown that the average penis size is 13cm we assume a penetration depth of 11cm. As the average duration we'll take the average time from entering the vagina - or wherever it enters ;) - to ejaculation - no foreplay. The average duration is found to be 11min . Finally we'll set the speed to "Normal" first and to "Fast" later.
Feeding the above values to the Sexdistance interface gives 53 meters in normal speed whereas 71 meters in fast. These numbers obviously are not the same for everyone and it varies among different people as it is based purely on average values and not in exact ones. Every individual should measure his/her own sex distance on sexdistance.
It needs no explanation the fact that the sex distance of the giver is the same for the receiver. In this particular case the distance covered by the penis inside the vagina is equal to the distance travelled by the vagina around the penis. Remember the piston image?
Measuring ones sex distance is a fun thing to do and the fact that it is so easy to do it with sexdistance.com makes it almost imperative to do so. Have fun!