How long is a .NET DateTime/TimeSpan tick?

Although currently a tick is 100 nanoseconds, it is best not to rely on this as an absolute. Rather, use 'TimeSpan.TicksPerSecond' (or any of the other TicksPerXxx member values)

The tick is the unit of granularity for the .NET DateTime and TimeSpan value types.

It has the following common conversions:

1 tick = 100 nanoseconds
       = 0.1 microseconds
       = 0.0001 milliseconds
       = 0.0000001 seconds

To quote MSDN:

The smallest unit of time is the tick, which is equal to 100 nanoseconds.

Metrology fail.

Note that, although the theoretical resolution of DateTime.Now is quite high, the resolution - ie how often it is updated - it quite a bit lower.

Apparently, on modern systems, DateTime.Now has a resolution of 10 milliseconds... See msdn.microsoft.com/en-us/library/system.datetime.now.aspx