The exact measurement is disputed amongst scholars with distances being given range between 6 to 15 kilometers. I have compiled this from various internet sources.
Monier Williams Sanskrit-English Dictionaryयोजन (
i.e. a distance traversed in one harnessing or without unyoking ;
esp. a
partic. measure of distance , sometimes regarded as equal to 4 or 5 English miles , but more correctly = 4 क्रोशs or about 9 miles ; according to other calculations = 2 1÷2 English miles , and according to some = 8 क्रोशs)
RV. &c
तथा च स्मर्यते योजनानां सहस्त्रं द्वे द्वे शते द्वे च योजने एकेन
निमिषार्धेन क्रममाण नमोऽस्तुते॥" Oh sun bow to you, you who traverse
2,202 yojanas in half a nimesha.".
A yojana
is said to comprise either 4 or 8 krosha (a cry or shout, or the range
of the voice in calling); and 1 krosha (or goruta as far as a cow’s
lowing may be heard, or a bull’s roar) may represent either 1000 or 2000 Danda ), and 1 danda represents 1 pauruSa (a man’s length) which
equals 1 dhanvantara (bow-string) or dhanu (bow). 1 yojana measures
either 4,000 or (more likely) 8,000 dhanus. Assuming that 1 paurusha is 6
ft long, then 1 yojana must represent a distance of about 14.6 km (or
about 9 miles, as suggested by Monier-Williams).
Wilson Sanskrit English Dictionary
योजन A measure of distance equal to four Kro4sas, which at 8000 cubits or
4000 yards to the Krosa , will be exactly nine miles; other
computations make the yojana but about five miles, or even no more than
four miles and a half.
Please see this link for Krosa.
http://en.wikipedia.org/wiki/Kos_%28unit%29
Swami Prabhupada gives the equivalent length of a yojana as 8 miles (13 km)
SB 5.16.7According to Ramayana
utsmayitvaa mahaabaahuH prekshya ca asti mahaabalaH |
paada a.nguSTena chikshepa sa.mpuurNam dasha yojanam || 1-1-65
Baali was able to throw Dundubhee Raakshas' body, with whole of his foot,
up to two hundred bow-lengths, where the length of bow is said as
six to seven feet. But Raam could kick that heap (of his bones) to 10 Yojan far,
roughly ninety miles, only with a flip of His big toe's tip. But Sugreev
continued his grumbling, 'in those days this skeleton was with
flesh and blood, now it has become weight-less, thus show me more of your
show of strength...'
One Yojan is an ancient measure for distance,
where that distance is covered in one yoking. Chambers Dictionary puts
it as five miles, and it is disagreeable for it is British-Indian
revenue measure. Traditionally it is four Krosh and thus each Yojan
is 9-10 miles.
According to Arthshastra
Arthshastra
says that 1
yojana = 4
gorutas;
1
goruta = 1000
dhanus; 1
dhanu = 96
angulas. Taking
the
angula as ¾ inch makes the
yojana about 4.54 statute miles.
During the colonial period the British administration set the
yojana at 5
miles; however, this seems to be smaller than its usual value. The ancient
commentator on the
Arthaśāstra says the
goruta is 2000
dhanus, which would make the
yojana about 9 miles.
Please see this Link for Aurel Stein's, T. W. Rhys Davids. views
http://www.sizes.com/units/yojana.htm