The fair place to meet is Albuquerque, NM — the city closest to the midpoint of Boise and San Antonio. From the farther side that’s about 16 hr 19 min of driving.
Recommended midpoint
Albuquerque, NM
From Boise
16 hr 19 min
779 mi to Albuquerque
From San Antonio
12 hr 55 min
616 mi to Albuquerque
San Antonio has the shorter trip; the split is off by about 3 hr 24 min. The alternatives below can even it out. Boise and San Antonio are about 1,383 miles apart.
Boise and San Antonio are about 1,383 miles apart by road. Split the difference and you arrive near Albuquerque, the city closest to the halfway point between them. That puts roughly 16 hr 19 min of driving on the Boise side and 12 hr 55 min on the San Antonio side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Albuquerque still makes a fair, central place for Boise and San Antonio to converge, splitting the travel instead of asking one side to cross the country.
If Albuquerque doesn't have what you're after, Denver and El Paso are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Boise and San Antonio.
Albuquerque is the most populous city in the U.S. state of New Mexico. Founded in 1706 as La Villa de Alburquerque by Santa Fe de Nuevo México governor Francisco Cuervo y Valdés, and named in honor of Francisco Fernández de la Cueva, 10th Duke of Alburquerque… Read more →
Boise is the capital and most populous city in the U.S. state of Idaho. It is the county seat of Ada County. The population of the city was 235,685 at the 2020 census. Read more →
San Antonio is a city in the U.S. state of Texas. It is the seventh-most populous city in the United States, the second-most populous city in Texas, and the second-most populous city in the Southern U.S., with a population of 1.43 million at the 2020 census. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.