What actually counts as a circuit
A circuit is a single dedicated wiring run protected by its own breaker, not just an outlet. Lighting is usually split into at least two circuits so one fault doesn't take out every light in the house. General power is typically split by area or level. Then high-draw appliances, ovens, hot water systems, air conditioning, and EV chargers, each need their own dedicated circuit rather than sharing with general power points.
Why older homes are so under-circuited
Homes built before the 1990s were often wired with as few as 4 to 6 circuits covering the entire property, because the appliance load back then was genuinely lower. No air conditioning, no EV charger, far fewer powered devices per household. That board wasn't wrong when it was installed, it just hasn't kept pace with what a modern household actually plugs in.
What pushes the number up
Every major addition to a home tends to need its own circuit, not a share of an existing one. An EV charger needs a dedicated circuit. A reverse cycle air conditioning system usually does too. Solar and battery systems add their own circuits again. Add a renovation with a bigger kitchen, and appliance-heavy circuits multiply further. None of these are optional extras from a safety standpoint, running high-draw equipment off a shared circuit is exactly what causes nuisance tripping and, in worse cases, overheating.
It's also worth remembering that circuits aren't just about capacity, they're about isolating faults. A board with plenty of circuits means a single fault, a failed appliance or a damaged cable, only ever takes out one small part of the home rather than everything at once.
How this gets decided on your property
There's no single right number, it depends on the size of the home, what's currently installed, and what you're planning to add. This is why a proper circuit assessment happens on site rather than over the phone, an electrician needs to see the existing board and understand what you're trying to run before recommending how many circuits, and how much total capacity, your switchboard actually needs. If you're seeing warning signs already, see our 7 warning signs guide.