AllGo has several high-profile backers, including Mr. Sturgell, the American plus-size model Tess Holliday and Roxane Gay, the writer whose recent b ook, “Hunger,” ex plores in intimate detail what it feels like to walk through the world as a 6-foot-3-inch woman who at one time weighed more than 500 pounds.

“I want to enjoy the cocktails and the gorgeous food being put before us,” Ms. Gay, 44, writes about a dinner date with friends, “but all I can think about is the pain in my thighs and the arms of the chair pinching my sides and how much longer I will have to pretend everything is fine.”

Supporting Ms. Alexander’s new app was an easy call, Ms. Gay said. “It opens the world up to have an app that will tell fat people how accommodating or not various spaces are,” she said. “I don’t think that restaurateurs even know this is something they need to think about.”

Discussing strategies to help bigger customers is something many restaurants are loath to do, either because they don’t have one or because they don’t want to link their food with obesity.

Waffle House, a 2,100-unit restaurant chain based in Georgia that has been criticized for its calorie-heavy menu, offers mostly booths and fixed counter seating. But it also provides larger diners free-standing chairs at counters and tables.

The company would not discuss those decisions. “We are a private company and keep to ourselves when it comes to our strategies,” said Pat Warner, its director of public relations.

Many chains have added movable furniture, wider booths and chairs that meet industry standards for people who weigh as much as 400 pounds. Some accommodations are made to satisfy requirements laid out in the Americans with Disabilities Act, but not specifically for larger customers. Courts have held that obesity constitutes a disability under some circumstances, but it remains an emerging area of law.