Whether you’re throwing the outdoor wedding of the season with 200 guests or managing a construction project with 75 workers, you’ll want to have enough portable restrooms to accommodate nature’s call. Overestimate the number and you’ll overspend. Underestimate and your guests or workers could stand in a long line for the loo — and, worse, have to hold their nose when their turn comes.

So how many port-a-potties will you need to keep your crowd clean and comfortable? The group at United Rentals can help you decide the right number, whether you’re renting single plastic units or luxury restroom trailers. But here are a few tips.

How many people, for how long?

The main factors to consider are the number of people who will use the restrooms and the number of hours for which you’ll need them. At construction sites and other industrial settings, the standard ratio is one port-a-potty per 10 workers in a 40-hour work week, said Jerry Vecchiarelli, regional product development manager at United Rentals. The ratio may be more flexible for commercial uses.

The OSHA Sanitation Standard for Construction requires the following:

• For 1 to 20 workers: At least 1 toilet
• For 20 to 190 workers: At least 1 toilet seat and 1 urinal for every 40 workers
• For 200 or more workers: 1 toilet seat and 1 urinal per 50 workers

For events lasting up to four hours, as a general rule of thumb, provide at least one portable restroom per 50 people. That ratio may differ for larger crowds and longer events. For specifics, see the chart.

Will alcohol be served?

Demand for restrooms will rise if alcohol is served. If it is, consider adding 10 percent to 20 percent more port-a-potties.

Will permanent restrooms be available?

Investigate the permanent restroom facilities that may be available at the site. These, of course, will reduce the need for portable restrooms.

Are there women on the jobsite?

On construction projects that include women workers, the National Association of Women in Construction recommends providing separate facilities for them.

Meeting the Americans with Disabilities Act requirements

Brush up on these requirements:

There should be at least one handicap-accessible restroom, for instance, and one handicap-accessible restroom for every 20 portable restrooms (a ratio of 5 percent). The path to the restroom must also be accessible, clear of curbs, steps or other impediments for people with disabilities.

You should provide equal services for all attendees, so if you opt for higher-end trailers, your handicap-accessible restrooms should be trailers, too.

Keeping it clean

For jobsites and for events of long duration, maintenance and service of port-a-potties is key.

"The pain points are typically related to service if you have a company that does not properly service the unit," Vecchiarelli said. "That involves washing down the interior, pumping out the wastewater tank, recharging the tank with chemical deodorizer and water, replenishing toilet paper and other paper products, and replacing the hand sanitizer. That typically happens once a week, and if that doesn't happen at least once a week, that's going to be a problem."

Whatever the occasion, dirty or insufficient restrooms can leave a lasting negative impression. On the jobsite, a shortage of toilets can even cut into productivity. So crunch the numbers with care. Providing the right number of facilities, properly serviced, makes the inevitable bio break comfortable, convenient, and — unless you’re aiming to impress your guests with a luxury restroom experience — perfectly forgettable.

Visit the United Rentals marketplace to rent equipment today and find tools you need for a better worksite.