Six quick rules from Craig Rental Works in Lancaster, PA.
For an event of up to 4 hours. 100 guests = 2 standard units.
6 hours or more: about 1 extra unit per 100 guests.
If the chart says 5 units and beer is served, book 6.
ADA section 213.2: at least 5% of units in each cluster, never fewer than 1.
Use the free calculator or call. Same-day delivery in Lancaster County by 12 pm.