Strabo reported that Pytheas said he "travelled over the whole of Britain that was accessible".
Because there is scant first hand sources available regarding Pytheas's journey, historians have looked at the etymology for clues about the route he took up the north Atlantic.
 The word epelthein, at root "come upon", does not imply any specific method, and Pytheas did not elaborate.
He did use the word "whole" and he stated a perimetros ("perimeter") of more than 40,000 stadia.
Using Herodotus' standard of 600 feet (180 m) for one stadium gives 4,545 miles (7,314 km); however, there is no way to tell which standard foot was in effect.
The English foot is an approximation.
Strabo wanted to discredit Pytheas on the grounds that 40,000 stadia is outrageously high and cannot be real.

Diodorus Siculus gave a similar number: 42,500 stadia, about 4,830 miles (7,770 km), and explains that it is the perimeter of a triangle around Britain.
The consensus has been that he probably took his information from Pytheas through Timaeaus.
Pliny gave the circuitus reported by Pytheas as 4,875 Roman miles.

The explorer Fridtjof Nansen explained this apparent fantasy of Pytheas as a mistake of Timaeus.
Strabo and Diodorus Siculus never saw Pytheas' work, says Nansen, but they and others read of him in Timaeus.
Pytheas reported only days' sail.
Timaeus converted days to stadia at the rate of 1,000 per day, a standard figure of the times.
However, Pytheas only sailed 560 stadia per day for a total of 23,800, which in Nansen's view is consistent with 700 stadia per degree.
Nansen later states that Pytheas must have stopped to obtain astronomical data; presumably, the extra time was spent ashore.
Using the stadia of Diodorus Siculus, one obtains 42.5 days for the time that would be spent in circumnavigating Britain. (
It may have been a virtual circumnavigation; see under Thule below.)

The perimeter, according to Nansen based on the 23,800 stadia, was 2,375 miles (3,822 km).
This number is in the neighborhood of what a triangular perimeter ought to be, but it cannot be verified against anything Pytheas may have said, nor was Diodorus Siculus very precise about the locations of the legs.
The "perimeter" is often translated as "coastline", but this translation is misleading.
The coastline, following all the bays and inlets, is 7,723 miles (12,429 km) (see Geography of the United Kingdom).
Pytheas could have travelled any perimeter between that number and Diodorus'.
Polybius added that Pytheas said he traversed the whole of Britain on foot, of which he, Polybius, was skeptical.
Despite Strabo's conviction of a lie, the perimeter said to have been given by Pytheas is not evidence of it.
The issue of what he did say can never be settled until more fragments of Pytheas literature are found.
Strabo reported that Pytheas said he "travelled over the whole of Britain that was accessible". Because there is scant first hand sources available regarding Pytheas's journey, historians have looked at the etymology for clues about the route he took up the north Atlantic.  The word epelthein, at root "come upon", does not imply any specific method, and Pytheas did not elaborate. He did use the word "whole" and he stated a perimetros ("perimeter") of more than 40,000 stadia. Using Herodotus' standard of 600 feet (180 m) for one stadium gives 4,545 miles (7,314 km); however, there is no way to tell which standard foot was in effect. The English foot is an approximation. Strabo wanted to discredit Pytheas on the grounds that 40,000 stadia is outrageously high and cannot be real.
Diodorus Siculus gave a similar number: 42,500 stadia, about 4,830 miles (7,770 km), and explains that it is the perimeter of a triangle around Britain. The consensus has been that he probably took his information from Pytheas through Timaeaus. Pliny gave the circuitus reported by Pytheas as 4,875 Roman miles.
The explorer Fridtjof Nansen explained this apparent fantasy of Pytheas as a mistake of Timaeus. Strabo and Diodorus Siculus never saw Pytheas' work, says Nansen, but they and others read of him in Timaeus. Pytheas reported only days' sail. Timaeus converted days to stadia at the rate of 1,000 per day, a standard figure of the times. However, Pytheas only sailed 560 stadia per day for a total of 23,800, which in Nansen's view is consistent with 700 stadia per degree. Nansen later states that Pytheas must have stopped to obtain astronomical data; presumably, the extra time was spent ashore. Using the stadia of Diodorus Siculus, one obtains 42.5 days for the time that would be spent in circumnavigating Britain. (It may have been a virtual circumnavigation; see under Thule below.)
The perimeter, according to Nansen based on the 23,800 stadia, was 2,375 miles (3,822 km). This number is in the neighborhood of what a triangular perimeter ought to be, but it cannot be verified against anything Pytheas may have said, nor was Diodorus Siculus very precise about the locations of the legs. The "perimeter" is often translated as "coastline", but this translation is misleading. The coastline, following all the bays and inlets, is 7,723 miles (12,429 km) (see Geography of the United Kingdom). Pytheas could have travelled any perimeter between that number and Diodorus'. Polybius added that Pytheas said he traversed the whole of Britain on foot, of which he, Polybius, was skeptical. Despite Strabo's conviction of a lie, the perimeter said to have been given by Pytheas is not evidence of it. The issue of what he did say can never be settled until more fragments of Pytheas literature are found.
Pytheas