How the Calculator and Cost Ranges Work
Last reviewed:
This page explains what the restroom calculator does with your answers, which numbers come from published sources, which are our own planning estimates, and where the costs page prices come from. Everything runs in your browser; nothing you enter is sent anywhere.
What the calculator asks
A guest count (clamped to 10–1,000), the event type (ceremony only, cocktail reception, or full dinner reception), the duration (under 4 hours, 4–6 hours, or 6+ hours), whether alcohol is served, and, for outdoor weddings, the season.
Step by step
1. Base ratio by event type
The guest count is divided by 100 for a ceremony only, 50 for a cocktail reception, and 40 for a full dinner reception: the wedding formulas in the FAQ of the Stahla Services restroom trailer size guide (published December 30, 2020), which calls them the minimum stalls needed. The guide also gives a general rule of 1 stall per 50 guests for a 4–6 hour event, and looser wedding ratios elsewhere (1 stall per 75–100 guests for a ceremony); we use the stricter FAQ divisors.
2. Alcohol: multiply by 1.2
Stahla's size guide says to add 20% more capacity for events serving alcohol or lasting longer than 6 hours, and estimates that alcohol service raises restroom use by 15–20%. United Site Services' event planning guide also says guests use restrooms more when alcohol is served, without a percentage.
3. Six hours or longer: multiply by 1.2
This comes from the same Stahla sentence. A long event that also serves alcohol gets both factors (×1.44). That stacking is our choice: Stahla does not say whether to combine them, and its FAQ offers adding one extra stall instead. Events under 4 hours get no reduction.
4. Outdoor summer weddings: multiply by 1.1
This 10% bump is our planning estimate. We did not find a published source for a heat or hydration factor, so treat it as a cushion, not a rule.
5. Round up, minimum two stalls
The result is rounded up to a whole stall, with a floor of 2. The floor is our choice: Stahla's chart starts at a 1-stall trailer for 25–75 guests, but a second stall lets two guests go at once during peak moments.
6. Match the stall count to a trailer
The calculator picks the smallest of 2, 3, 4, 6, 8, or 10 stalls that covers the count, and above 10 combines 10-stall trailers with one smaller unit. This mapping is ours. Stahla's guest-count chart is much less conservative (a 2-stall trailer for 75–150 guests, a 4-stall for 200–300), so expect our answer to run a size or two larger than a vendor's chart.
7. Accessibility guidance
The calculator suggests 5% of your stalls as accessible, rounded up, with a minimum of one. The 5% figure comes from the 2010 ADA Standards, §213.2 Exception 3: where single-user portable toilet units are clustered at one location, no more than 5% of the units in each cluster need to comply with the accessible toilet-room requirements in §603. Accessible units need a turning space inside the room (§603.2.1): a circle 60 inches in diameter minimum (§304.3.1) or a T-shape within a 60-inch square.
The Standards set no wedding-specific rule. They apply to facilities covered by the ADA, such as public accommodations and state and local government facilities, so whether they apply depends on the venue and host, and a multi-stall trailer is not the same as a cluster of single-user portable units. Our 5% suggestion is planning guidance, not a legal determination: if any guest uses a wheelchair, rent at least one unit the vendor confirms meets §603, and ask your venue what it requires.
Worked examples
We ran these through the calculator's actual code (lib/calculator.ts). Each needs 1 accessible stall, since 5% of 20 or fewer stalls rounds up to 1.
| Event | Math | Stalls | Trailer |
|---|---|---|---|
| 150 guests, dinner reception, alcohol, 4–6 hours, indoors | 150 ÷ 40 = 3.75 × 1.2 = 4.5 | 5 | 6-stall |
| 220 guests, dinner reception, alcohol, 6+ hours, outdoors in summer | 220 ÷ 40 = 5.5 × 1.2 × 1.2 × 1.1 = 8.71 | 9 | 10-stall |
| 80 guests, cocktail reception, alcohol, under 4 hours | 80 ÷ 50 = 1.6 × 1.2 = 1.92 | 2 | 2-stall |
| 120 guests, ceremony only, no alcohol, under 4 hours | 120 ÷ 100 = 1.2 (raised to the 2-stall minimum) | 2 | 2-stall |
| 500 guests, dinner reception, alcohol, 6+ hours, outdoors in summer | 500 ÷ 40 = 12.5 × 1.2 × 1.2 × 1.1 = 19.8 | 20 | 2 × 10-stall |
Where the price ranges come from
The ranges on the costs page are our planning estimates for a single-day wedding rental; no single source publishes them. We cross-checked them against the price guides below, which vary widely by vendor and region and do not all use the same terms (per day, per event, or per weekend).
| Size | Our range | Published figures |
|---|---|---|
| 2-stall | $800–$1,500 | $800–$1,500 for 2–3 stalls (The Lavatory); $900–$1,200 (Mobile Thrones); $500–$1,000 per day for 2–3 stalls (360Connect); $2,799 per event (Stahla) |
| 3-stall | $1,000–$1,800 | $1,200–$1,500 (Mobile Thrones); $800–$1,500 for 2–3 stalls (The Lavatory) |
| 4-stall | $1,200–$2,200 | $1,500–$1,800 (Mobile Thrones); $1,000–$2,500 for 4–6 stalls (The Lavatory, 360Connect); $3,399 per event (Stahla) |
| 6-stall | $1,500–$2,800 | $1,000–$2,500 for 4–6 stalls (The Lavatory, 360Connect) |
| 8-stall | $2,000–$3,500 | $2,500–$5,000 per day for 7+ stalls (360Connect); $2,500–$8,000 for 7+ stalls (The Lavatory); $4,799 per event (Stahla) |
| 10-stall | $2,500–$4,500+ | Same 7+ stall ranges as above; $5,699 per event (Stahla) |
Sources: The Lavatory (Arizona rental company), Mobile Thrones (published April 22, 2025), 360Connect, and Stahla's 2026 pricing guide (price table marked updated October 15, 2026). Our ranges overlap some of the published regional figures, but Stahla's list prices are well above them: its event rate covers Friday delivery to Monday pickup, with setup ($1,499 per trailer) and pack-up ($999) on top. Treat our low ends as optimistic.
What the ranges leave out
These can appear on a quote on top of the base rental. Ask about each:
- Delivery distance. Stahla says delivery within 25 miles usually costs nothing extra, then about $2.99–$3.99 per mile; The Lavatory quotes about $3–$4 per mile past a 25–50 mile free radius.
- Setup and pack-up fees. Some providers include them (Mobile Thrones says its pricing includes delivery, setup, and pickup in its service area) and some bill them separately (Stahla).
- Power and water. Without hookups, Stahla and The Lavatory both list generators at $150–$300 per day and water delivery at $100–$250 per service.
- Attendants. The Lavatory bills attendant service hourly on top of the rental; we found no published rate.
- Peak season. Stahla says prices rise 15–30% in peak season (May–October) and carry holiday-weekend premiums.
- Climate control. 360Connect says it adds $100–$500 depending on trailer size.
- Taxes, deposits and damage or cleaning fees. Ask whether the quote is all-in.
Limits of this tool
The calculator gives a planning estimate, not a quote or a compliance check, and vendors' rules of thumb differ widely: United Site Services' wedding page suggests one standard porta potty for every 8 guests, and its event guide says fewer than 250 people for under four hours need three or four units (single portable toilets, not trailer stalls). Your county, city, or venue may set its own sanitation, permit, or accessibility requirements, and those take priority over this site.
How often we review these figures
Every figure and link here was checked against its source on October 16, 2026. We recheck at least every six months and whenever the calculator changes, and update the date at the top. All sources are on the sources page; our editorial policy explains corrections.
How this site works, in four pages: