Here are the measurements. The base is irregularly shaped ( five sided). I'll do my best. Head is on port side. The outboard side is 20" fore and aft. The forward side is 17 1/2". The aft side is 16". The inboard edge is 17". The height is 5". There's a diagonal cut (fifth side) on the inboard aft corner that explains the discrepancy in measurements. Hope this helps.