Panel & Breaker Spaces

Notes

• **Code minimum and real houses are different numbers.** NEC 210.11(A) asks for only 13 circuits here, because it counts general lighting as watts per square foot. No modern house is wired that way — a builder puts in roughly one circuit per 350 ft² plus dedicated runs, which comes to **18**. Both numbers are on this page because comparing your own panel against the code minimum will make you think the maths is wrong.
• **"How many breakers fits a 200 amp panel" has no single answer** — slot count is a property of the panel model, not of the service size. A 200 A panel comes in 20, 30, 40 and 42-space versions. The useful question is how many slots *this house* needs, and that is **21**.
• **Slots are not circuits.** Every two-pole breaker — range, dryer, water heater, air conditioner, EV charger — takes **two** slots. Here 18 circuits occupy 21 slots. Counting circuits and buying a panel to match is why a "40-space" panel fills up at circuit 28.
• **Buy about 20% spare.** Every house adds circuits: a hot tub, a garage sub-feed, a heat pump, a charger. Adding slots later means a subpanel or a whole new panel, and both cost far more than the difference between a 30-space and the next size down at install time.
• **Tandem breakers are not a free upgrade.** They fit two circuits in one slot, but only where the panel label permits them and only in the positions marked. A panel stuffed with tandems beyond its listing is a failed inspection and a real hazard — the busbar was not designed for it.
• Slot count and service size are two independent constraints. A 100 A service can fill a 40-space panel; a 200 A service can run out of room in a 20-space one. Size the service by load, size the panel by slots, and do not let one answer stand in for the other.