According to the Rugby Union laws,
Field of play -- 100m (min 94m)
In-goal -- 6m~22m (under the former laws, "as close to 22m as possible, at least 10m if possible, minimum 6m". When changed?)
Width -- 70m (min 68m)
I suggest:
106m (94m+6m+6m) --minimum
112m (100m+6m+6m)
120m (100m+10m+10m)...