Which is the best estimate for the lenght Of a real baseball bat?

The length of the bat is probably about 34 in.

Inches is not an SI unit

The SI unit for length is the metre (m)

So to convert from inches to metres the following conversion factors are used:

34 in = 34in x (2.54cm / 1 in) x (1m / 100cm)

= (34 x 2.54 : 1 x 1 : 100) (in x cm : in x m : cm)

=0.8636 m

3 ft < because a wilsons bat is 3 ft