The fair place to meet is Detroit, MI — the city closest to the midpoint of Milwaukee and Pittsburgh. From the farther side that’s about 5 hr 17 min of driving.
Recommended midpoint
Detroit, MI
From Milwaukee
5 hr 17 min
252 mi to Detroit
From Pittsburgh
4 hr 18 min
205 mi to Detroit
Pittsburgh has the shorter trip; the split is off by about 59 min. The alternatives below can even it out. Milwaukee and Pittsburgh are about 445 miles apart.
Milwaukee and Pittsburgh are about 445 miles apart by road. Split the difference and you arrive near Detroit, the city closest to the halfway point between them. That puts roughly 5 hr 17 min of driving on the Milwaukee side and 4 hr 18 min on the Pittsburgh side — the fairest single meeting point among the cities near the middle.
That's a half-day drive from each side, so Detroit suits an overnight or a weekend rather than a quick coffee — long enough to want a reason to stay, short enough to drive.
If Detroit doesn't have what you're after, Cleveland and Columbus are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Milwaukee and Pittsburgh.
Detroit is the most populous city in the U.S. state of Michigan. It is situated on the bank of the Detroit River across from the Canadian city of Windsor, Ontario. It is the 26th-most populous city in the United States and the largest U.S. Read more →
Milwaukee is the most populous city in the U.S. state of Wisconsin. It is located on the western shore of Lake Michigan at the confluence of the Milwaukee, Menomonee, and Kinnickinnic Rivers. Read more →
Pittsburgh is a city in Allegheny County, Pennsylvania, United States, and its county seat. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.