All solar, battery and generator calculators
Every calculator on the site, grouped by job. Each one shows the formula behind the result and works in US or metric units where units matter.
Loads & energy use
- Solar Load CalculatorAdd up appliance watts × hours into watt-hours a day, amp-hours from the battery and peak watts — the number every solar and battery size starts from.
- Watts to Amps CalculatorWatts to amps (and back) at 12, 24, 48, 120 or 240 V — including the battery current an inverter pulls for an AC load.
- Electricity Cost CalculatorWhat an appliance costs to run per hour, day, month and year from its watts, hours and your price per kWh.
Batteries
- Battery Runtime CalculatorHow long a battery runs a load: amp-hours, voltage and chemistry against watts, with inverter loss and duty cycle.
- Amp-Hours to Watt-Hours CalculatorConvert battery amp-hours to watt-hours or kWh (and back) at 12, 12.8, 24 or 48 V, with the usable share for LiFePO4 or lead-acid.
- Battery Bank Size CalculatorBattery bank size in amp-hours at 12, 24 or 48 V from daily watt-hours or an inverter load, with usable depth of discharge for LiFePO4 or lead-acid and the number of batteries.
- Power Station Runtime CalculatorHow long a portable power station runs a fridge, heater, CPAP, Starlink or fan, from its watt-hours, the load and the inverter loss.
- Home Backup Battery CalculatorHow many kWh of battery to keep a house (or just the essentials) running through an outage, and how many battery units or 100 Ah batteries that is.
Solar panels
- Solar Panel CalculatorHow many solar panels you need: array watts and panel count from your daily watt-hours, peak sun hours, system losses and battery losses.
- Solar Panel Output CalculatorHow much power a solar panel produces per day, month and year from its watts and your peak sun hours — plus amp-hours into a battery.
- Off-Grid Solar System CalculatorSize a whole off-grid system at once: battery bank, solar array, charge controller and inverter from your daily watt-hours, sun hours and biggest loads.
- Solar Panels for One ApplianceHow many solar panels to run a refrigerator, freezer, mini-split, window AC, pool pump or CPAP — from its watts and hours, with typical ranges if you don’t know them.
- Charge Controller Size CalculatorWhat size solar charge controller you need: MPPT output amps from array watts and battery voltage, or PWM amps from the array’s short-circuit current.
- Solar Battery Charge Time CalculatorHow long a solar panel takes to charge a battery: sun hours and days from the battery’s amp-hours, how flat it is, panel watts and your peak sun hours.
- Solar Panel Series & Parallel CalculatorArray voltage, current and watts for solar panels in series, parallel or both — with the cold-weather open-circuit voltage from the panel’s temperature coefficient.
- Solar Panel Tilt Angle CalculatorThe tilt angle for solar panels from your latitude — fixed all year, or adjusted for winter and summer — and which way to face them.
Home solar & EVs
- Solar System Size CalculatorHome solar size from your electric bill: system kW and number of panels to cover your monthly kWh, using NREL PVWatts output for your area.
- EV Solar Charging CalculatorHow many solar panels to charge an electric car: kWh per day from your daily miles and the car’s EPA efficiency, and the panels to match.
- Solar Payback CalculatorHow many years a grid-tied solar system takes to pay for itself, from its cost, incentives, yearly kWh and your electricity price.
Inverters & generators
- Inverter Size CalculatorWhat size inverter you need: continuous watts for everything running at once, surge watts for motor starts, and the DC amps it pulls from a 12, 24 or 48 V battery.
- Generator Size CalculatorWhat size generator you need: running watts for everything on at once plus the biggest motor’s starting surge, with headroom.
- RV Generator Size CalculatorWhat size generator for a 30 amp camper or 50 amp RV: running and starting watts for the air conditioners plus everything else, against the rig’s service.
- Generator Fuel & Runtime CalculatorHow long a generator runs on the fuel you have — gasoline, diesel or propane — and how much it burns per hour at your load, from its spec-sheet run time.
- Propane Tank Runtime CalculatorHow long a 1, 20, 30, 40 or 100 lb propane tank lasts on a heater, grill, stove or fridge, from the appliance’s Btu rating.