Joules to Watt-hours Converter

When to use joules → watt-hours

Joules to watt-hours divides by 3600, since 1 Wh = 3,600 J (one watt sustained for one hour). A 54,000 J phone-battery discharge is 15 Wh — right on spec for a typical smartphone battery. Electronics datasheets quote capacity in Wh or mAh, while physics work stays in joules, so this conversion sits at the lab-to-product boundary. Don't confuse watts with watt-hours: a watt is power (J/s), a watt-hour is energy — mixing them is the classic battery-spec mistake.

Electronics designers calculating the energy stored in a capacitor from ½CV² work in joules, then convert to watt-hours when sizing that storage against a battery-backup budget. A supercapacitor charged to hold 18,000 J stores 5.000 Wh, comparable to a small backup power bank. Because capacitor energy is usually tiny compared to battery capacity, this conversion mainly matters in hybrid energy-storage designs where joule-scale capacitor bursts and watt-hour-scale battery reserves need to sit on the same footing during a system energy budget.

How to convert joules to watt-hours

1. 1

   Take your value

   Start with your value in joules.

2. 2

   Multiply by 0.000277778

   Multiply the joule value by 0.000277778. This is the exact conversion factor from joules to watt-hours.

3. 3

   Read the result

   The product is your value in watt-hours. For example, 5 J × 0.000277778 = 0.00138889 Wh.

Conversion formula

The exact factor from joules to watt-hours is 0.000277778.

Watt-hours = Joules × 0.000277778

Joules to Watt-hours conversion table

Fifty common reference values, hand-picked for skim utility. Use the calculator above for any value not listed.

Real-world reference

A heartbeat releases about 1 J of mechanical work. Lifting an apple 1 m takes roughly 1 J.

Frequently asked questions

How many watt-hours are in 1 joule?

1 joule equals 0.000277778 watt-hours.

How do I convert joules to watt-hours?

Multiply the joule value by 0.000277778. So x J × 0.000277778 = the equivalent in Wh.

What is 5 joules in watt-hours?

5 joules equals 0.00138889 watt-hours.

What is 10 joules in watt-hours?

10 joules equals 0.00277778 watt-hours.

What is 100 joules in watt-hours?

100 joules equals 0.0277778 watt-hours.

How do I convert back from watt-hours to joules?

Multiply the watt-hour value by 3600. For example, 1 Wh = 3600 J.

Is the joule bigger than the watt-hour?

No. 1 joule is smaller than 1 watt-hour. It takes 3600 joules to equal 1 watt-hour.

Are these conversion factors exact?

The factor is derived directly from the SI definitions of joule and watt-hour; the displayed value is rounded for readability, and the browser computes using IEEE 754 double-precision arithmetic.

About the joule and the watt-hour

Sources

• NIST Special Publication 811 — Guide for the Use of the International System of Units (SI)
• BIPM — SI Brochure (9th edition)
• Reverse: Wh to J
• All energy converters