Watts to Joules
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Watts to Amp-hours (Ah) Calculator

Calculate required battery capacity (Ah) from power (Watts), voltage, and time.

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How Watts to Ah works

Amp-hours (Ah) measure the electric charge capacity of a battery. To size a battery for a device, you need to know how many watts it draws, the battery voltage, and how long you want to run it.

First calculate the Watt-hours (Wh = Watts × Hours), then divide by the battery voltage to get Amp-hours.

Formula
1Ah = (Watts × Hours) ÷ Volts

Used for deep-cycle, RV, and marine battery calculations.

Watts to Ah conversion table

Reference Table4 rows
Watts to Ah for a 12V battery running for 1 hour.
Power Draw↕Time↕Battery Voltage↕Required Ah↕
50 W
1 hr
12 V
4.17 Ah
100 W
1 hr
12 V
8.33 Ah
500 W
1 hr
12 V
41.67 Ah
1000 W
1 hr
12 V
83.33 Ah
💡 Click any row to auto-fill the calculator aboveClick column headers to sort

FAQ: Watts to Ah

How do you convert watts to amp-hours?

Multiply the watts by the hours the device will run, then divide that result by the battery voltage.

How many amp hours is a 100 watt solar panel?

A 100W solar panel produces around 8.33 amps at 12 volts in perfect sunlight. Over 5 hours of sun, it generates roughly 41.65 amp-hours of charge into a 12V battery.

Tools related to Watts to Ah

Watts to Joules ConverterThe full power × time energy calculator with three modes.kWh to JoulesTurn the kWh figure on your electricity bill into joules — 1 kWh = 3,600,000 J.Joules to kWhConvert a joule or megajoule figure into billable kilowatt-hours — divide by 3,600,000.Watts to AmpsCalculate amps from watts and volts for DC and AC circuits — I = P ÷ V.Joules to CaloriesConvert joules into calories and food Calories (kcal) — 1 cal = 4.184 J.Watts to VoltsCalculate volts from watts and amps for DC and AC circuits — V = P ÷ I.Amps to WattsCalculate watts from amps and volts for DC and AC circuits — P = V × I.Watts to OhmsCalculate ohms from watts and volts or amps — R = V² ÷ P.Joules to WhConvert joules into watt-hours — divide by 3,600.Joules to eVConvert joules into electronvolts — 1 eV = 1.602×10⁻¹⁹ J.Joules to BTUConvert joules into BTUs — 1 BTU ≈ 1,055 Joules.Joules to WattsCalculate watts from joules and time — W = J ÷ seconds.Electricity CostFind out exactly how much an appliance costs to run on your electric bill.Ah to WattsConvert battery amp-hours into sustained watts — W = (Ah × V) ÷ Hours.Watts to HPConvert watts into mechanical horsepower — 1 HP ≈ 745.7 Watts.HP to WattsConvert mechanical horsepower into watts — W = HP × 745.7.