We hope to construct, to the best of our ability, a time line for the Buddha's life. To do so, one of our most important research tasks is to establish how he conducted his teaching activities throughout northern India in the forty-five years following his enlightenment. The Buddhist scriptures tell us that he travelled one or two yojanas a day. Unless we can convert the yojana into modern units of measurement, though, such descriptions are of little use to us. Existing theories concerning the length of a yojana say it is anything from 4 km to 23 km, and there is still no agreement. This essay makes a close study of the length of the yojana, using descriptions given in various Indian works, in Chinese records of travels by Chinese monks to India, such as the Datang xiyuji (A Record of the Western Regions in the Great Tang) and the Faxian zhuan (Biography of Faxian), and in the Vinaya regulations. The summary below paraphrases the Conclusion.

1. We first study the nature of the yojana as a unit of distance.

1-1. The yojana is the longest unit of length in the ancient Indian system of weights and measures. It is based on smaller units such as the aṅgula (or aṅguliparva), the vitasti and the hasta. The aṅgula is said to be the distance between two joints of a finger and the vitasti is the length between the tip of the thumb and the tip of the little finger when the hand is extended. Twelve aṅgula make one vitasti. The hasta is the distance from the elbow to the tip of the fingers; two vitasti make one hasta (see the measurement chart at the end of the volume). The dhanu is the next unit of length and is considered to be a person's height, and equivalent to four hasta. However, the size of a finger and the length from elbow to fingertip differ according to person. The same goes for a person's height. There may thus be inconveniences when standardizing something where there are such individual differences. For example, since there is a danger of a person who is taller than average hitting his head on the head jamb, if his house is built to suit the dimensions of the average sized person, the house should be built larger than the standard. This is what Henmi Baiei (1891-1977), a Buddhist art historian, called "relative measurement" (mātrāṅga). If a lifesize statue is to be made of a specific person, then both aṇgula and hasta will accord with that person's actual measurements. However, if units of measurement to be used as standard differ from person to person, they cannot fulfil their role, and so a standard length must be determined. This is what Henmi Baiei termed "absolute measurement" (mānāṅga). For example, according to the Buddhist Vinaya Pitaka, the hasta is considered to be sugatavidatthi; this means that the standard height of a Buddhist statue is three times lifesize, that is, sixteen shaku (ca 16 feet; Jap. jōroku) tall. Since the Vinaya determined this as the standard, it can function adequately as a linear measure.
1-2 In this way, the sub-units of the yojana were formed based on parts of the human body. Of course they were standardized when used as measurements, but the human physique tends to grow as time passes. For example, if we continue to use a standard based on the average height being 150 cm, even when the average has increased to 170 cm, people will inevitably hit their heads on head jambs. Since this is inconvenient in a unit of measurement, we may surmise that the length of the hasta and the dhanu gradually increased. In a similar context, it can be proved historically that in China the chi and the bu grew gradually larger.
1-3 When parts of the body were made into units of measurement, like the hasta and the dhanu, it was probably easy to produce a comparative standard scale. However, when we come to units of length used for measuring distance, like the krośa and yojana, it must have been more difficult to construct such a scale in an age when no theory of measurement had been established. For example, even if it was decided that one yojana was ten km, if the technology to measure ten km accurately did not exist, people would have to rely either on their own measurements or their own sense of distance. That units for large distances were given names that certainly expressed sensory units, like krośa, which means the distance the mooing of a cow can be heard, and yojana, which means the distance a yoked beast can pull a burden, speaks eloquently of this. The yojana was not originally an exact figure but one based on the physical senses. It is thus risky to interpolate our own sense of measurement, born of the age in which we live.
1-4 Nevertheless, we can recognize that in the Vinaya the yojana was clearly an objective unit for measuring distance. Rule 16 of the nissaggiya-pācittiya (Expiation with forfeiture) rules in the Vinaya says that a bhikkhu may carry wool for three yojanas, but not one step more. Here, yojana is treated as a categorical unit of length. If there was no technique to measure it, then it could be nothing more than a subjective distance; by specifying "three yojanas" the regulation consciously accepts this measurement as an absolute unit.

2. The yojana is thus characterized as a standardized unit to measure distance. However it was used at times expediently, and even speculatively.

2-1 It is common knowledge that the distances appearing in guidebooks to Buddhist sites in India are not very accurate. For example, many people go to Saheth Maheth, but there are probably very few who can say how many metres separate Maheth (the site of the Jetavana monastery) and Saheth (the dwelling of Sudatta). Neither did Faxian and Xuanzang travel around India measuring the land like the Japanese surveyor and cartographer, Ino Tadakata (1745-1818), did, and so it is unsafe to treat the "yojana" recorded in their travel records and the "yojana" as an absolute scale of measurement. When we attempt to investigate the length of the yojana as an objective unit of distance, we have to consign their records as works of secondary importance.
2-2 Actual travel, however, is not the same as the distances shown on a map. Roads are not straight but are deflected by rivers and mountains. Seasons and weather, as well as a traveller's physical condition, also influence the journey. This means that even the subjective yojana experienced physically is not without value. In fact, in view of the purpose of this essay, to know the distance the Buddha travelled in a day, it actually has a high utility value.

3. Taking the above basic points into consideration, I would like to draw the following conclusions about the themes taken up in this essay.

3-1 There were two types of yojana as a unit of distance in India: the "small yojana" of 4,000 dhanu and the "large yojana" of 8,000 dhanu. The former was used in Magadha and the latter in northern India. The two types derived from differences in units - whether one yojana was considered to be 4 krośa or 8 krośa, and whether one krośa was considered to be 500 dhanu or 1,000 dhanu.
3-2 According to the information about India left in the travel records of the Tang period Chinese monks, Yijing and Xuanzang, two types of yojana were in use at the time: the "sacred" yojana and the "secular" yojana. Though one was not exactly twice the size of the other, like the small and large yojanas referred to above, they were close. Probably the "sacred" yojana was the yojana stipulated in the Vinaya and corresponded to the "small" yojana of Magadha, while the "secular" yojana was that used widely in India at the time, and corresponded to the "large" yojana used in "northern India". There is a certain inevitability that idea of "sacred" and "Buddhist" should be associated with Magadha. We do not know why the two types of measurement unit came into use. It may be that as time passed people grew in physique and so the unit lengthened. However there is no possibility that people's physique doubled, and since it does not appear that the length of the dhanu and hasta changed, this explanation does not hold. However, because in the Vinaya regulations the yojana appears in a legal sense, with associated penalties, it could not be easily changed. We can probably say, therefore, that the "small" yojana represents the length of the yojana in the ancient period.
3-3 The "small" yojana as a unit of distance was about 6.5 km and the "large" yojana was about 13 km. These are figures arrived at considering the physique of people in ancient India and the length of the Tang period li. Also, there is no consistency in the length of the "small" yojana being 6.5 km even when we look it applied to the regulations in the Vinaya.

4. As a result of an analysis of the travel records of Chinese monks such as Faxian and Xuanzang and of descriptions contained in the early Pali sutras and their later commentaries (aṭṭhakathā), we find that one yojana, as distance physically experienced, corresponds to around 11.5 km. Since these records and descriptions presumably had the "secular" yojana in mind, it must originally have been equivalent to the "large" yojana; but given that the "large" yojana was 1.5 km longer, it probably reflects the subjective distance experienced by travellers carrying heavy luggage. In addition, due also to the presence of rivers and mountains, and the vagaries of wind and rain, met with during the course of the journey, even a shorter distance than the standard was experienced as one yojana. Because we began this investigation in order to know how fast the Buddha moved during his wandering life, we cannot ignore this result. If we state that the Buddha travelled an average of one yojana a day, he must have been able to walk around 11.5 km each day. It would therefore have taken 56.5 days to travel between Rajagaha and Sāvatthi, separated by a distance of about 650 km along the Ganges. We infer that the Buddha would have traveled around between the middle of the eleventh month and the middle of the second month the following year, in terms of the ancient Chinese calendar; according to the modern calendar, this approximates the three months between the beginning of February and the end of April. It would have been impossible to make a return journey between Rajagaha and Sāvatthi in that time.