Every calculator FigureDesk has shipped so far, grouped by category. Each one shows the formula it used and asks for the values only you know — a battery's depth of discharge, an inverter's rated efficiency — rather than assuming a default. All of them are free, run entirely in your browser, and don't require an account.
Solve for voltage, current, resistance, or power from any two values.
Convert power to current for DC, single-phase, or three-phase AC.
Convert current to power for DC, single-phase, or three-phase AC.
Convert between apparent power (kVA) and real power (kW) using your equipment's actual power factor.
Calculate the current-limiting resistor value and power rating for an LED.
Read a 4-band or 5-band resistor's color bands to find its resistance and tolerance.
Calculate output voltage, current, and resistor power for a two-resistor voltage divider.
Calculate how much it costs to run an appliance per day, month, and year.
Calculate total energy use for one or more devices per day, week, month, and year.
Calculate power factor and reactive power from real and apparent power readings.
Calculate total and per-phase power for a balanced three-phase system, wye or delta.
Size an inverter from your continuous load and largest single starting surge.
Estimate how long a battery will run a given load, from capacity, voltage, and depth of discharge.
Calculate the battery capacity needed to run a load for a target number of hours.
Estimate the battery capacity needed to cover your daily energy use for a chosen number of autonomy days.
Estimate the solar array size and panel count needed to offset your daily energy use, from your own peak sun hours and system losses.