Here are the numbers if you guys want them (rounded to a sensible decimal place):

Radius of earth = 6 000 km (so diameter = 12 000 km)
Mean depth of oceans = 4 km
Deepest depth of ocean = about 11 km (Mindanao Trench)
Highest peak of mountains (for comparison) = about 9 km (Mount Everest)

Ratio of mean ocean depth to Earth's diameter = 4 / 12000 = 0.0003

So a globe of diameter 1m (3.28 feet) would have ocean depth of 0.3 mm = 12 thousandths of an inch. You can scale this for whatever size globe you like.

Just doing my oceanographical duty. Cheers!