I love this question as it appears regularly in Answers.com. Please remember that these are IRB (International Rugby Board) regulations and they stipulate maximums for this subject.
Dimensions. The field of play does not exceed 100 metres in length and 70 metres in width. Each in-goal does not exceed 22 metres in length and 70 metres in width.
The in goal areas of 22 metres times 2 is added to the in play area of 100 meters giving an overall of 144 metres
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