Off-grid electrics calculators

60 free calculators for 12 V, 24 V and 48 V systems in campervans, RVs, boats, cabins and sheds. Size batteries, solar panels, inverters, cables and fuses, then check your numbers before you buy.


Batteries

Capacity, run time, bank sizing, voltage charts and conversions.

Amp hours to watt hours calculatorConvert battery Ah to Wh and kWh at any voltage.Watt hours to amp hours calculatorConvert Wh or kWh to amp hours at any battery voltage.mAh to Wh calculatorConvert power bank and cell mAh to watt hours (airline limits too).Battery run time calculatorHow long a battery will power a load, for lead-acid or lithium.Battery bank size calculatorHow many amp hours you need for your daily use and days of autonomy.Battery series and parallel calculatorTotal voltage, Ah and Wh when wiring batteries in series or parallel.Battery voltage and state of charge calculatorEstimate state of charge from resting voltage, lead-acid or LiFePO4.Battery C-rate calculatorConvert between C-rate and amps for charging and discharging.Peukert's law calculatorHow high currents reduce real lead-acid capacity and run time.Trolling motor battery calculatorRun time of an electric outboard or trolling motor on your battery.UPS runtime calculatorHow long a UPS or battery backup will keep your equipment running.Battery cost per cycle calculatorCompare the true lifetime cost of LiFePO4 and lead-acid batteries.E-bike battery range calculatorRange per charge from battery Wh and your riding style.

Solar

Panel sizing, output, charge controllers, string voltage and tilt.

Solar panel size calculatorHow many watts of solar (and how many panels) you need.Solar panel output calculatorDaily Wh, Ah and monthly kWh a panel or array really produces.Solar charge controller size calculatorPick the right MPPT or PWM controller current rating.MPPT string voltage calculatorCheck panels in series won't exceed your controller's max voltage when cold.Solar panels in series or parallel calculatorArray voltage, current and watts for any series/parallel layout.Solar panel tilt angle calculatorBest panel angle for year-round, summer and winter use.Off-grid solar system calculatorSize batteries, panels, controller and inverter in one go.Solar panel temperature loss calculatorHow much output a solar panel loses when it gets hot.How many solar panels fit on my roof?How many panels fit on a van, RV or shed roof, and total watts.Daylight hours and sun angle calculatorDay length, noon sun height and best panel angle for any date.

Inverters, loads & power

Inverter and generator sizing, energy use, hook-up and running costs.

12 V power consumption calculatorAdd up your appliances to find daily Wh and Ah for a van, RV or boat.Inverter size calculatorContinuous and surge rating for your appliances, plus DC current.Inverter current draw calculatorHow many amps an inverter pulls from your battery, plus fuse size.Portable power station run time calculatorHow long a power station will run your devices, and recharge time.Generator size calculatorGenerator watts and kVA for your running and starting loads.Hook-up and shore power calculatorWhat you can run on a campsite EHU or 30A/50A RV pedestal.Electricity cost calculatorDaily, monthly and yearly running cost of any appliance.12 V fridge power consumption calculatorDaily Ah of a compressor fridge, how long the battery lasts, and solar needed.CPAP battery calculatorHow many nights a battery or power station will run a CPAP machine.Generator fuel consumption calculatorFuel per hour and run time per tank for petrol, diesel or propane generators.

Cables & fuses

Voltage drop, cable sizing in mm² and AWG, fuses and wire resistance.

DC voltage drop calculatorVoltage lost in a DC cable run, in volts and percent.DC cable size calculatorPick the right 12 V, 24 V or 48 V cable size in mm² or AWG.AWG to mm² converterConvert wire gauge to mm², diameter and resistance, with a full chart.Fuse size calculatorChoose a fuse that suits the load and protects the cable.Wire resistance calculatorResistance of copper or aluminum cable by length, size and temperature.AC voltage drop calculatorVoltage drop on 230 V or 120 V cables, hook-up leads and extension reels.

Charging

DC-DC chargers, battery charge time and solar charge time.

Battery charge time calculatorHow long a charger takes to fill a lead-acid or lithium battery.DC to DC charger size calculatorChoose a battery-to-battery charger to suit your alternator and battery.Solar battery charge time calculatorHow many sunny days or hours solar takes to charge your battery.Battery charging voltage calculatorAbsorption, float and cut-off voltages for LiFePO4 and lead-acid at 12/24/48 V.

Heating, gas & water

Heater sizing, diesel and gas use, insulation, water tanks and rainwater.

BTU to watts converterConvert BTU/h, watts, kW, kcal/h, horsepower and tons of cooling.Diesel heater fuel consumption calculatorDiesel per hour and per night, tank life and battery use of a diesel air heater.Propane tank and gas bottle calculatorHow long a propane or butane bottle lasts on a heater, hob or fridge.Van, caravan and cabin heat loss calculatorHeat loss in watts and BTU, and the heater size you need.Insulation R-value and U-value calculatorR-value (metric and US) and U-value for common insulation materials.Water tank capacity calculatorTank volume in litres and gallons, and how many days your water lasts.Rainwater harvesting calculatorRainwater you can collect from a roof per year and month.Water heating time and energy calculatorTime, kWh and battery Ah to heat water with an element, kettle or immersion.

Wind

Small wind turbine output, wind at height and wind speed units.

Wind turbine power calculatorPower and rough annual energy from a small wind turbine.Wind speed at height calculatorHow much faster the wind blows higher up a mast.Wind speed converterConvert mph, km/h, knots and m/s, with Beaufort force.

Electrical basics

Ohm's law, watts, amps and volts.

Ohm's law calculatorEnter any two of volts, amps, ohms or watts to find the rest.Watts to amps calculatorConvert watts to amps for DC, single-phase or three-phase AC.Amps to watts calculatorConvert amps to watts for DC, single-phase or three-phase AC.LED resistor calculatorSeries resistor value and wattage for LEDs on 12 V or 24 V.kVA to kW and amps calculatorConvert kVA, kW and kVAR, and find the current for single or three phase.Energy unit converterConvert kWh, Wh, joules, BTU, kcal and therms.

Plan a system in four steps

  1. Add up your daily energy use with the power consumption calculator.
  2. Size the battery bank to cover that use with the battery bank calculator.
  3. Size the solar array and charge controller with the off-grid solar system calculator.
  4. Choose cables and fuses with the DC cable size and fuse size calculators.

Every calculator works in both metric and imperial units, shows the formula it uses, and runs entirely in your browser.