Sarna lists the Mammoth as 277 meters in diameter, so if you loaded the Overlord Add-on in HMMap, and then edited its size to 277 meters, that would be pretty close. Sorry, I don't have a real top-down view of the Mammoth, and a quick search of the Net only produced 3/4 or size views. But the scaling suggested will get you in the ballpark.
Basically, it will take up about 9x9 hexes, or 1/4 of a standard map sheet.
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