AmpSize
A cable size calculator and 84 more for New Zealand and Australia. Each result cites its clause and table.
Every calculator is free. No account needed to calculate.
Android app on Google Play- Size a cable for a shedThe smallest cable that carries the load over the run to a shed.
- Size a submain for a tenancyThe smallest three phase submain that passes each check, on AU 3008.1.1:2025.
- Size a battery cableThe d.c. cable size for a 3 m, 48 V battery run at 100 A.
- Size a cable for an EV chargerThe cable size for a 32 A charger on a 25 m run.
- Wire a houseRooms and points become circuits, cable sizes and a maximum demand.
- Check a long run for voltage dropThe voltage drop on the run, against the limit.
AmpSize in 30 seconds
One job in the cable size calculator, from the inputs to a result you can keep.
Sorted for all trades
Calculators
85 calculators
Cables
- Cable size
- Voltage drop
- Loop impedance
- Fault rating
- Conduit fill
- Voltage rise
- Underground cable
- Segregation and separation
- Maximum circuit length
- Simplified selector
- Minimum conductor size
- Imperial cable
- Comms cable selector
- Aerial clearances
- Site cord length
- Loop power budget
- DC cable size
- Correction factors
- Total voltage drop
- Conductor colours
- Cable tray fill
- Cable loss cost
Protection
Loads
Power
Solar
Safety
Guides
All guides- Builder's pole: supply, RCDs and cord lengthsA builder's pole for a house build, worked to AS/NZS 3012:2019. The supply it may take, the 30 mA RCDs, the Table 1 cord lengths and the test intervals.
- Car-park floodlight: obtrusive light at a boundaryTwo 10 000 lm floodlights 10 m from a neighbour's window in zone A2, checked against AS/NZS 4282 for lux at the window, candela and the upward light ratio.
- Homeowner shed supply voltage drop over 60 mA 20 A single‑phase supply running 60 m to a shed on 6 mm² copper, with the drop, the percentage and the maximum length the AmpSize voltage drop engine returns.
- Commercial kitchen kW to amps full load currentTurning a 30 kW commercial kitchen nameplate load into 45.58 A at 400 V three phase, with the power factor step that a plain kW to amps sum leaves out.
- Generator fault current calculation at 400 VA 500 kVA 400 V standby set at 12 % subtransient reactance gives 721.69 A full load and 6014.07 A fault current, with the decay the figure leaves out.
- IEEE 1584-2002: arc flash model and limitsWhat the IEEE 1584-2002 empirical model governs, where it stops applying, and a 400 V switchboard study that lands on 7.54 cal/cm² at 455 mm.
Learn
All learn pages- Conduit fill and installation methodsHow the conduit space factor works, what the fill percent means against the 40 % limit, and how the install method names on site map to the 3008 columns.
- Current-carrying capacity and deratingWhy one cable size has many ratings. Install method, ambient, grouping, soil and depth, with a 25 A circuit that needs 10 mm² once the factors apply.
- Downlights and insulation: IC-4, CA90 and Non‑ICThe six recessed luminaire classes, what insulation may do around each, which a NZ or AU home may have, the default clearances, and the roof space warning sign.
- Home batteries and AS/NZS 5139How a home solar battery is sized in kWh, what usable, nominal, depth of discharge and round-trip efficiency mean, and where AS/NZS 5139 lets one go.
- Home battery location and clearancesWhere AS/NZS 5139 lets an all-in-one home battery go. Restricted places, 600 and 900 mm zones, the habitable room barrier, ceiling, IP codes and working space.
- How many circuits can go on one RCDThe AS/NZS 3000 Cl 2.6.2.4 arrangement rules in plain words, which circuits need a 30 mA RCD in NZ and AU homes, how RCBOs count, and why the rules exist.