Electrical calculators & guides
Free electrical tools and plain-English guides for United States — each gives the answer fast and shows the working behind it.
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.