The baseline rule
One toilet stall per 50 guests for a four-hour event. This assumes a typical event with food service, soft drinks, and modest alcohol consumption.
Quick reference table
| Guests | 4-hr event (base) | 6-hr event | All-day event |
|---|---|---|---|
| 50 | 1 stall | 1 stall | 2 stalls |
| 100 | 2 stalls | 3 stalls | 3 stalls |
| 150 | 3 stalls | 4 stalls | 5 stalls |
| 200 | 4 stalls (1 unit) | 5 stalls | 6 stalls |
| 300 | 6 stalls | 7 stalls | 8 stalls (2 units) |
| 400 | 8 stalls (2 units) | 9 stalls | 10 stalls |
| 500 | 10 stalls | 12 stalls (3 units) | 14 stalls |
Adjustments that increase stall count
- Alcohol service for the full event: +15–20% capacity
- Each hour beyond 4: +10–15% capacity per additional hour
- Heavy food service (long buffet, multi-course meal): +10% capacity
- Demographic skew (older guests, parents with young children): +10–15%
- Outdoor summer event (heat = more hydration): +10% capacity
Worked examples
Wedding — 150 guests, 6 hours, alcohol all night, summer
- Baseline 150 guests = 3 stalls
- +1 stall for the 5th and 6th hours
- +1 stall for full alcohol service
- Total: 5 stalls — book one 4-stall trailer + on-site attendant
World Cup watch party — 100 guests, single match window (~3 hours)
- Baseline 100 guests at 3 hours ≈ 2 stalls
- Tight bathroom-trip clustering at halftime: +1 stall
- Total: 3 stalls — one 4-stall trailer is the right call
Gala — 350 guests, formal seated dinner, 5 hours
- Baseline 350 guests = 7 stalls
- +1 for the 5th hour and the formal pace of bathroom trips
- +1 for full alcohol service
- Total: 9 stalls — book two 4-stall trailers + 2 attendants