Sri Ramanuja Munaye Namaha,
Sri Velukkudi Krishnan Swami Guruve Namaha,
Dear BhagavAta,
Based on Sri Velukkudi Swami’s Arul and Asmadh Acharyan’s Krupai and Google Acharyan’s support, here are some facts regarding 1 Yojana = how many miles.
Shastras DOESN’t use the British Imperial system of measurement units,
Like we use ‘Inches’, and British defined the inches as 1/12th of “A feet”, and that Feet is the length of Roman King foot. So, how to decide the length of Roman King’s foot, how long is his foot is?. So, British ‘BenchMarked” that Roman Kings’ feet as 1 Feet, then divided 1/12th of his feet as 1 inch and so on broke down to cm and mm.
Shastras smallest Unit is ‘Angulas”. The present day “inches” are termed based on this Angulas
1 Angula = Breadth of a Human Finger (Not the breadth of thumb)
Here is the General Formula as per Shastras for Angulas to Yojanai
1 angula = ‘X’ of present day inch; 4 angulas = 1 dharnugraha [bow grip]; 8 angulas = 1 dhanurmuSTi [fist with thumb raised]; 12 angulas = 1 vitasta [spandistance of stretched out palm between the tips of a person’s thumb and little finger]; 2 vitastas = 1 aratni / hasta; 4 aratnis = 1 danDa / dhanus; 10 danDas = 1 rajju; 2 rajjus = 1 paridesh; 2000 dhanuss = 1 krosa / goruTa 4 krosas = 1 yojana 
So, over all 768000 Angulas = 1 Yojanai.
Now, coming back to converting Angulas to inches, the length of a feet changes from yuga to yuga and even it redcues from century to century within the kali yuga. So , if we keep a 1 foot scale on our feet, our feet is samller than the actual 1 feet scale, so we can imagine, how much longer the Roman kings feet were in old days which matches the 1 feet scale.
Hence, during time to time, when Acharyas/Yuga Purushas calculate the “Angulas” to that present day Inches, the value of the “Conversion factor” keeps changing”, since they consider the AVERAGE feet length of humans in that period as 1FEET.
Ramanujar avataram period was 1017~1137 CE, and Britain/England was formed only recently around 1603, so Acharyas defintion as per Angulas = Breadth of a finger (other than Thumb).
Swami Ramanujar was 8 feet tall approx based on present calcualtions, we could imaging Swamis finger breadth, 1 Angula = 2.09cm (Its no wonder). So, based on the Shastras formula, 1 Yojana = 10miles. Present day Acharyas recently SriPerumputhur Swami in 1873 period made the Brahmamdam image, where Swami has mention 1 Yojana = 8 miles, which means 1 Angula = 1.68cm, which is approx same as present day humans finger breadth.
 Sri Velukkudi Swami’s answer of 1 Yojana = 10 miles is based on Swami Ramanujar’s finger breadth of 1 Angula =2.09cm.
 And later Acharyas/Maha Purushas after 1137CE (around 1800 CE) has defined as 1 Yojana = 8 miles, based on their period finger breadth of 1 Angula = 1.68cm.
 There are also some conversions, where other Sanatana Dharma acharyas calculated 1 Yojana = 9 miles. Means their finger breadth of 1 Angula = 1.88cm.
 In order to get 1 Yojana = 5miles as BhagavAta mentioned, the conversion should have been done in very recent times, where their finger breadth of 1 Angula = 1.05cm.
 Literally, If we consider 1 Angula = 1 Inch (12.54cm), then 1 Yojana = 12.1miles.
Here is conversion factor of Inches based on the breadth of finger (1 Angula) measurements at different periods.
if 1 angula = 0.41 inch = 1.05cm, then 1 yojana =5 miles ==> 
if 1 angula = 0.66 inch = 1.68cm, the 1 yojana =8 miles ==> 
if 1 angula = 0.74 inch = 1.88cm, the 1 yojana =9 miles ==> 
if 1 angula = 0.825 inch = 2.09 cm, the 1 yojana =10 miles ==> 
if 1 angula = 1 inch = 2.54 cm, the 1 yojana =12 miles ==> 
1 Yojana =
768000 Angulas

If 1 Angula =
below Inches

inch to miles conversion factor 
Miles 
X 
Y 
Z 
X x Y x Z 
768000 
0.415 
1.58E05 
5.0 
768000 
0.66 
1.58E05 
8.0 
768000 
0.74 
1.58E05 
9.0 
768000 
0.825 
1.58E05 
10.0 
768000 
1 
1.58E05 
12.1 
If we need to get the actual definition of 1Feet and to know how much is it in present day inches, then we need to check on North Side, where there is SriRama’s SriPadha Impression in a rock, then we can divide BhagavAn’s feet length to 12 sections and that 1 section should be the actual 1 inch.
Then, we will get the actual value of 1 Yojana = how many miles.
Even the Distance of Braha loka (Sathya lokam) inside one Andam has a Measurement value in Yojanas as per Vishna Purana. However, adiyen personally believe, the Value of 1 yojana = 5 or 8 or 9 or 10 or 12 miles are immaterial for Prapannas, since our Destination SriVAikuntam is beyond any measurement, and the only route to Moksham SriVaikuntam is our Swami ramanujar ThiruvAdi and we ALL will travel through ArchaRaadhi maargam with Asmadh Acharya Krupai and Sri Velukkudi Swami’s Abhimaanam in this same janma.
Sri Vishnu Loka (SriVaikuntam) Mani mandappa maarga (Route) dhayee, Ramanujou vijayathey Yathiraja rajaha:
Adiyen Sri Velukkudi Krishna Dasan,
Uyya Oraey Vazhi UdayavAr ThiruvAdi,
Sarvam Sri Krishna Kudumbham.