Electrical calculators & guides
Free electrical tools and plain-English guides for New Zealand — each gives the answer fast and shows the working behind it.
Solar panel calculator
How many solar panels do I need? Enter your monthly kWh, peak sun hours and panel wattage — get the system size in kW and the number of panels to fit.
Open tool →Voltage drop calculator
Will my wire drop too much voltage? Enter the current, run length and wire size — get the % drop checked against the 3% / 5% guideline, in AWG or mm², copper or aluminium.
Open tool →Wire size calculator
Can I run 14 gauge wire on a 20 amp circuit? Pick your wire gauge, breaker size and conductor — get an instant safe/not-safe check against NEC Table 310.16 ampacity.
In the worksGenerator size calculator
What size generator do I need? Select the appliances you want to run — get the running load, starting-demand peak and the recommended generator size instantly.
Open tool →About electrical calculations
Electrical calculations are unforgiving because the failure modes are invisible until they matter: a conductor sized too small doesn't look wrong, it just runs hot. The everyday questions — how much voltage a long run loses, what a circuit can safely carry, how loads add up across a panel — all reduce to well-established formulas using conductor resistance, length, and current.
The electrical tools here work from those standard physical constants and published resistance values, showing every step of the working. They are deliberately conservative where rounding is involved: when a result sits on a boundary, the safer interpretation is shown.
Using the results
Electrical work is regulated nearly everywhere, and rightly so. Use these results to plan, estimate, and check someone else's arithmetic — then have the design confirmed against the wiring rules in force where you are, and use a licensed electrician where your jurisdiction requires one. The calculator tells you what the physics says; your local rules decide what you're allowed to install.