Compact toilets are designed for tight bathrooms — powder rooms, half-baths, and small primary bathrooms where the standard toilet projection (29–31 inches from wall to front of bowl) intrudes on walking clearance or door swing. The two compact strategies are: (1) compact-elongated bowls that retain elongated ergonomics but with a shorter overall projection (~27 inches), and (2) round-front bowls (~26 inches projection) that give up some seating comfort for maximum space savings.
The compact-elongated designs are the better choice for most use cases — you keep the comfort of an elongated bowl while saving 2 inches of bathroom depth. Top compact-elongated picks: American Standard Edgemere Compact-Elongated ($329–$429), Kohler Cimarron Compact ($349–$449), DeerValley DV-1F0026 Compact ($349–$419), Delta Riosa Compact ($299–$369), Kohler Gleam One-Piece Compact-Elongated ($329–$429).
Round-front compact picks (when the bathroom is so tight that compact-elongated still won't fit): American Standard Cadet 3 Round-Front ($229–$299), Niagara Liberty Round-Front ($259–$329), Glacier Bay All-in-One Round-Front ($199–$259).
Measure your bathroom layout before committing. If your toilet alcove has less than 27 inches of front-to-back clearance, you need compact-elongated or round-front. If less than 26 inches, you need round-front. Standard projection toilets (29+ inches) will physically fit in tight spaces but won't meet building code clearances.