Any normal lunch box fits a standard grocery bag

Yes — a regular rectangular lunch box, up to about 11 inches long and 8 inches wide, fits inside a standard reusable grocery bag with room to spare.

The typical reusable grocery bag (the polypropylene ones from Trader Joe’s, Target, Aldi, etc.) is roughly 13–15 inches tall, 12–14 inches wide, and 6–8 inches deep. A standard hard lunch box is about 9–10 inches long, 7–8 inches wide, and 4–5 inches tall. That’s a comfortable fit in every dimension.

The only things that won’t fit are oversized hard coolers (the 12-inch-plus behemoths) and tall insulated totes that are taller than the bag is deep. If you’re carrying the lunch box upright like a briefcase, you’ll also hit the bag’s height limit sooner — but laid flat, you’re fine.

Just don’t try to fit a six-pack of soda in there too.