How much is one pound of us half dollars worth?

Not a meaningful question. It depends on their dates and mint marks.

As a general rule, halves dated 1951-64 are worth about $7 for their silver content.

Halves dated 1965 to 69 are worth about $3. Anything from 1971 to today is a common circulation coin worth 50 cents.

If your halves are older than that you'll need to check them against a price guide such as the one at Numismedia.com