Electrical Load Estimation for a Residential Building
A wiring design that undersells or overestimates actual demand causes real problems either way. Here is how load estimation is actually done.
Connected load and demand load are different numbers
Connected load is the sum of every circuit's rated capacity if everything ran simultaneously at full draw - which almost never happens in practice. Demand load applies diversity factors that reflect realistic simultaneous usage, and it's demand load, not connected load, that should size the service entrance, main breaker, and distribution panel.
Sizing directly off connected load without applying diversity typically results in an oversized, more expensive installation; underestimating demand by guessing low does the opposite, sizing a panel that gets pushed past safe margins the moment real usage catches up to the actual building.
Room-by-room and circuit-by-circuit, not a single building-wide guess
A proper estimate breaks the building down by area and circuit type: general lighting and receptacle load per room, dedicated circuits for fixed appliances (air conditioning, water heaters, kitchen equipment), and any special loads like an EV charger or workshop equipment, each accounted for individually before summing with diversity factors applied.
Future load headroom is a design decision, not an afterthought
Panels sized to exactly match a building's day-one demand routinely run out of headroom within a few years as air conditioning, EV chargers, or additional circuits get added. Building in reasonable spare capacity at the design stage is far cheaper than a capacity upgrade later - see our guide on signs your panel needs upgrading for what happens when that headroom runs out.
This is a calculation, not a lookup table
Generic per-square-metre load figures exist and can be a rough starting point, but they don't account for a specific building's actual equipment, occupancy pattern, or planned additions. We run this as a real assessment against the building and its intended use, not a template applied regardless of what's actually in it.
Scope a job with our team
Tell us what you need engineered, repaired, or installed. We respond with a scoped assessment, not a guess.