It's seventy feet but only one metre (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

SONNET (poem with one verse formed of 14 lines each with 5 feet [in this case, pairs of stressed and unstressed syllables – 14 * 5 =70)  I’m no expert of feet and metres in poetry but there seems a slight confusion between the definitions I have used in the previous two lines.  The first definition is from Chambers Dictionary and the second is from an explanation of feet in a SONNET from a web search.