Australia works it out by group. America pools volt-amps.
Ask an American calculator for maximum demand and it will total up the connected volt-amps, apply a general demand factor to a chunk of it, and hand you one number. That is the NEC method and it is structurally different from ours.
AS/NZS 3000 assesses maximum demand for a domestic installation group by group. Lighting is worked from floor area. Socket outlets are worked in blocks of twenty points. A range, a fixed water heater and air conditioning each get their own allowance as a percentage of their connected load. You add the group results together and that total is the maximum demand.
The reason it works is that the groups behave differently. A water heater element is on at full load or off — no diversity worth counting. Forty socket points are almost never drawing anything like their rating at once. Pooling both into one factor loses that, which is why the Australian method keeps them apart.
A worked example
A 200 m² house with 40 socket points and a 9 kW electric range, single phase at 230 V:
- Lighting: 200 ÷ 100 × 3 A = 6 A
- Socket outlets: 10 A for the first 20 points, plus 5 A for the next block of 20 = 15 A
- Range: 9000 ÷ 230 = 39.13 A connected, at 50% = 19.57 A
- Maximum demand so far: 6 + 15 + 19.57 = 40.57 A → a 63 A mains
Now add the two things that get forgotten at quoting time:
- Fixed water heater 3600 W at 100%: 3600 ÷ 230 = 15.65 A
- Air conditioning 5000 W at 75%: 5000 ÷ 230 × 0.75 = 16.30 A
- New total: 72.52 A, which is 16.68 kVA → an 80 A mains
Two appliances took the job from 63 A to 80 A. That is the difference between a service that was already there and a service upgrade with a distributor application attached, so it is worth doing this sum before the quote goes out rather than after.
Standard mains ratings
| Rating | Single phase at 230 V | Where it usually lands |
|---|---|---|
| 40 A | 9.2 kVA | Small unit, gas cooking and gas hot water |
| 63 A | 14.5 kVA | The common older domestic service |
| 80 A | 18.4 kVA | Modern all-electric house with air con |
| 100 A | 23.0 kVA | Large house, pool, EV charging |
| 125 A and up | 28.8 kVA + | Usually a three-phase conversation instead |
Above about 100 A single phase the practical answer is often three phase rather than a bigger single-phase service, and the distributor will usually say so. Three phase spreads the same total demand across three conductors, so the per-phase figure — and the mains rating that follows from it — drops accordingly.
Why every allowance on this page is editable
Because the real tables are more specific than this tool is. AS/NZS 3000's maximum-demand provisions distinguish a single domestic installation from multiple domestic installations, from blocks of living units, from non-domestic work, and the allowance for the same group changes between them. This calculator does not ask which one you are on, so it ships the widely published single-domestic figures and lets you overwrite every one of them.
If you are doing a duplex, a block of units or anything commercial, the row that applies to you is a different row. Look it up and type the numbers in.
The ones people leave out
- EV chargers. A 7 kW single-phase charger is 30 A of connected load and it runs for hours. It belongs in "other fixed" at minimum, and on a lot of installations it drives the whole answer.
- Pool and spa equipment. Pump, heater, chlorinator. A spa heater alone can be 6 kW.
- Second ovens, induction, ducted air. Kitchens have grown and ducted systems draw a lot more than a single split.
- Solar and batteries. They do not reduce maximum demand — the installation still has to be safe on a cloudy evening with a flat battery — but export limits and inverter capacity are a separate conversation with the distributor.
- Counting GPOs wrong. A double outlet is two points. Getting that wrong on a 40-point house shifts a whole block of twenty.
What the number is actually for
Maximum demand decides the size of the consumer mains, the main switch and the metering, and whether the existing service can carry what the customer is asking for. It is also the number the distributor wants when an upgrade application goes in.
Electrical installation work in Australia must be carried out by a licensed electrician, and the certificate of compliance is theirs. Use this to get to a defensible figure fast on site so you can price the job honestly — then confirm the allowances against the standard before anything is ordered.
Worked out the demand. Now price the upgrade.
Yamate turns the mains, the board, the accessories and the hours into a quote the customer accepts on their phone, then an invoice, then a payment — with GST handled and the follow-ups chased for you.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberMaximum demand & mains size FAQ
How do you calculate maximum demand in Australia?
Group by group. Lighting comes from floor area, socket outlets from blocks of twenty points, and the range, water heater and air conditioning each get a percentage of their connected load. Add the groups together and that total is the maximum demand in amps.
What is the maximum demand for a typical 200 square metre house?
Roughly 40 A with lighting, 40 socket points and a 9 kW range, pointing to a 63 A mains. Add a 3.6 kW water heater and 5 kW of air conditioning and it climbs to about 72.5 A, which needs 80 A.
How many amps is a normal house service in Australia?
63 A single phase is the common older domestic service, 80 A is typical for a modern all-electric house with air conditioning, and 100 A appears on larger homes with a pool or EV charging. Above that, three phase is usually the better answer.
Is the American maximum demand method the same?
No. The NEC pools connected volt-amps and applies general demand factors. AS/NZS 3000 assesses each group separately with its own allowance. The two methods can give quite different answers for the same house, so use an Australian one here.
Do I count a double GPO as one point or two?
Two. Points are counted individually, so a double outlet is two 10 A socket outlet points. Getting this wrong can shift you a whole block of twenty and change the answer.
Does an EV charger change maximum demand?
Significantly. A 7 kW single-phase charger is about 30 A of connected load running for hours at a time. Put it in as a fixed appliance and expect it to drive the mains size on many existing installations.
Why can I edit all the allowances?
Because the real tables distinguish single domestic, multiple domestic, blocks of living units and non-domestic installations, and this tool does not ask which you are on. The defaults are the published single-domestic figures. If your job is something else, look up the right row and type it in.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Group structure and demand allowances follow published Australian guidance on the AS/NZS 3000 maximum-demand provisions for a single domestic installation, and can change between editions. Other installation types use different allowances — every figure here is editable for that reason. This tool does not size consumer mains for current-carrying capacity, voltage drop or fault loop impedance, and it does not replace the distributor's own requirements. Electrical installation work in Australia must be carried out by a licensed electrician; this is an estimating aid, not a design or a sign-off.