One cubic foot of helium can lift 0.062 pound, so 161.3 cubic feet of helium is needed to lift 10 pounds. A balloon containing this amount of helium must be approximately 6.75 feet in diameter at sea level.
Helium is a heavier but more stable lifting gas than hydrogen, which it replaced. One major problem with hydrogen gas is that it is extremely flammable. The German blimp Hindenburg, filled with approximately 6 million cubic feet of hydrogen, caught fire in 1937 as it was attempting to land in New Jersey. The resulting fire killed 36 people and was captured on film.