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Calculators

Voltage Drop CalculatorThe main calculator. DC, single-phase and three-phase, with reactance and temperature correction when you need them.
DC Voltage Drop CalculatorBattery, solar and automotive circuits at 12 V, 24 V and 48 V, where a few tenths of a volt matter.
AC Voltage Drop CalculatorSingle-phase and three-phase with power factor, conductor reactance and raceway type.
Cable Voltage Drop CalculatorCable runs in metres and conductor sizes in mm², for anyone working to metric cable data rather than AWG.
Wire Size CalculatorThe smallest conductor that stays inside your drop limit, shown against the ampacity the size carries.
Maximum Cable Length CalculatorHow far you can run a given conductor before the drop crosses your limit.
Resistor Voltage Drop CalculatorOhm’s law solved for voltage, current or resistance, with power dissipation and a series divider.
Voltage Drop ChartDrop per amp per 100 ft for every size and material, plus conductor resistance and ampacity tables.

Voltage Drop FormulaEvery formula, with each variable explained and its units named.
Voltage Drop CalculationFive worked examples, start to finish, with the arithmetic shown.
How to Calculate Voltage DropThe five-step method, and the three mistakes that cause most wrong answers.
How to Measure Voltage DropThe voltage drop test with a multimeter, and why it beats a resistance reading.
What Is Voltage Drop?What it is, why it happens, and what it does to equipment.
Voltage Drop in CableHow length, size, material and temperature each move the number.
Acceptable Voltage DropWhere 3% and 5% come from, and what status they actually have.
Copper vs Aluminium ConductorsThe resistance difference, size for size, and what it costs you.

Data, Assumptions and MethodWhere every number comes from and what the calculations assume.
All calculatorsIndex of every tool.
All guidesIndex of every guide.