Energy Converter: Joules, kWh, Calories, BTU & More

Energy Converter

Convert any energy amount between joules, kilojoules, calories, kilocalories (food Calories), watt-hours, kilowatt-hours, BTU, foot-pounds, electronvolts, therms, and megajoules using a single joule base with exact factors.

⚡Real Energy Presets

🔢Conversion Inputs

Energy amount to convert

Enter the number of the from-unit you want to convert.

From unit

To unit

Decimal places in results

Converted result 0

Joules 0 SI base energy (J)

Kilowatt-hours 0 electric billing unit

Calories (kcal) 0 food Calories

BTU 0 heating and cooling

📐Common Equivalents At A Glance

0Joules

0Kilojoules

0Watt-hours

0Calories (small)

📋Full Conversion Factor Table

Unit	Symbol	Joules Per Unit	Your Amount	Everyday Meaning
Enter a value above to see every unit converted from your input.

🍎Food And Nutrition Energy Reference

Food Item	Food Calories	Kilojoules	Joules
Apple, medium	95 Cal	397 kJ	397,480 J
Banana, medium	105 Cal	439 kJ	439,320 J
Slice of bread	80 Cal	335 kJ	334,720 J
Cup of rice, cooked	205 Cal	858 kJ	857,720 J
Chicken breast, 100 g	165 Cal	690 kJ	690,360 J
Chocolate bar, 45 g	235 Cal	983 kJ	983,240 J
Big fast-food meal	1,100 Cal	4,602 kJ	4,602,400 J
Daily 2,000 Cal diet	2,000 Cal	8,368 kJ	8,368,000 J

A nutrition label Calorie (capital C) is one kilocalorie, which equals 4,184 joules.

🏠Household Energy Reference (kWh)

Appliance Use	Kilowatt-hours	Megajoules	BTU
LED bulb, 10 W for 10 h	0.10 kWh	0.36 MJ	341 BTU
Laptop charge, full	0.06 kWh	0.22 MJ	205 BTU
Microwave, 15 minutes	0.25 kWh	0.90 MJ	853 BTU
Refrigerator, one day	1.50 kWh	5.40 MJ	5,119 BTU
Electric oven, 1 hour	2.30 kWh	8.28 MJ	7,849 BTU
Clothes dryer, one load	3.00 kWh	10.80 MJ	10,239 BTU
EV charge, 40 kWh pack	40.0 kWh	144.0 MJ	136,486 BTU
Home, one full day	30.0 kWh	108.0 MJ	102,364 BTU

🔥Heating BTU And Cross-Unit Comparison

Energy Source	BTU	Joules	kWh	kcal	Therms
1 BTU (match tip)	1	1,055	0.000293	0.252	0.00001
Space heater, 1 hr	5,118	5.40 M	1.50	1,291	0.051
Cooktop burner, 1 hr	9,000	9.50 M	2.64	2,270	0.090
Water heater, 1 hr	40,000	42.2 M	11.72	10,087	0.400
Home furnace, 1 hr	80,000	84.4 M	23.45	20,174	0.800
1 therm natural gas	100,000	105.5 M	29.30	25,217	1.000
Central AC, 1 day	288,000	303.9 M	84.40	72,626	2.880
MMBtu (1 million BTU)	1,000,000	1.055 G	293.07	252,164	10.000

⚙Full Formula Breakdown

Two-step methodEvery conversion goes through joules. First multiply the input by its joule factor, then divide by the target unit factor.

Step one to joulesjoules = value × factor(from). Example: 2 kcal × 4184 = 8368 J.

Step two from joulesresult = joules ÷ factor(to). Example: 8368 J ÷ 1055.06 = 7.93 BTU.

Joule (J)Factor 1. The SI base unit of energy, work, and heat. One newton-metre.

Kilojoule – MegajoulekJ = 1,000 J and MJ = 1,000,000 J. Metric multiples used on food labels and utility bills.

Calorie and kilocaloriecal = 4.184 J. kcal = 4,184 J. A food Calorie shown on labels equals one kcal.

Watt-hour and kWhWh = 3,600 J and kWh = 3,600,000 J, because energy = power × time.

BTU and thermBTU = 1,055.06 J. A US therm = 100,000 BTU = 1.05506 × 10^8 J of gas.

Foot-poundft-lb = 1.35582 J, a mechanical work unit still common in engineering.

Electronvolt (eV)eV = 1.602177 × 10^-19 J, the tiny energy an electron gains across one volt.

💡Practical Energy Tips

Food label tip: When a wrapper lists "Calories" with a capital C it means kilocalories. To read the same value in kilojoules, multiply the Calories by 4.184.

Utility bill tip: Electricity is billed in kWh and gas is often billed in therms. One kWh is 3.6 MJ and one therm is roughly 29.3 kWh, so compare both in joules to see true cost per unit of heat.

There’s energy all around, but depending on your location, you speak a different dialect. At home, maybe you read a nutrition label and estimate whether some snack will be worth the caloric price tag. Maybe when your utility bill arrives, you stare at the line for kilowatt-hours and wonder how much that abstract charge translate into heat compared to the therms listed on your furnace bill, a.k.a. British thermal units (BTUs).

In the kitchen: Calorie. From the utility company: kilowatt-hours. In the furnace manual: BTU. It’s a mishmash of random standards, and everything require translating before you can compare one thing to another. No matter what we call it, energy is simply energy. Whether you run on an apple or a tank of fuel, you’re expending the exact same amount of work and heat.

The Joule is the Universal Energy Unit

For this reason, the joule act as universal translator; it’s the SI base unit of everything from home appliances to particle physics. By plugging things into the calculator, you strip away all the confusing labels, reducing each input down to its joules-equivalent. Then it stretch that number out to whichever target unit you need. It does this in two steps to guarantee accuracy, rather than using those pesky direct-conversion factors hiding in the footnotes of textbooks.

It gets even more complicated because world of nutrition already has its system of measurements: the food industry refers to a kilocalorie (a thousand little calories, but called a Calorie with a big C) as a Calorie. If you’re trying to track how many calories you take in compared to the amount of mechanical work your body does each day, you should of be aware of that difference. Four thousand joules = one kilocalorie, which doesn’t sound like much until you consider that it takes several million joules of energy to walk a mile. Check out the chart of common foods in standard metric units from the page’s reference table to see how your diet plan numbers compare to actual physical work.

BTUs (British Thermal Units) reign supreme in many parts of the world, including the heating and cooling industry. One BTU is about amount of heat required to increase one pound of water by one degree Fahrenheit. While this makes BTUs a convenient unit for engineers, trying to match your electric bill against your gas bill using them can be frustrating. Many utilities sells natural gas by the therm (one therm equals one hundred thousand BTUs). That’s a huge chunk of energy when compared to most home appliances. Learning how they relate allows you to determine what type of improvements will affect your bottom line, i.e. Should I upgrade my insulation or switch out my appliances?

Another wrinkle: electrical energy combines power and time. Watts are a measure of power, yes… But a kilowatt-hour is a measure of how much power you used over an hour. That’s what a kilowatt-hour is. It’s easy to mix up watts with watt-hours which leads people astray when estimating solar panel production or battery life. One kilowatt-hour hold three point six million joules. Because each device appears individually low powered, your house consumption quickly adds up to this big number.

And on the other end of the spectrum, if you’re into semiconductor tech or physics, it will convert electronvolts to joules as well, that’s what an electronvolt is: the amount of energy picked up by an electron passing through a single volt of potential. Yes, it’s very tiny, but it’s the stuff that governs the absorption of solar cells and the release of energy in nuclear reactions. Converting this may seem ridiculous (bridging the gap from subatomic particles to furnace output!), but it show just how universally the joule can be used as a measuring stick.

It’s not so much about remembering the factors as it is getting perspective. When you realize that an hour of streaming your favorite show, a big meal, and a blast from your space heater have something in common the mysterious idea of utility bills dissapears. Suddenly, you’re thinking of energy in terms of one currency spent on many part of your life. The next time you glance at your bill or a product’s label, keep in mind that behind the confusing acronyms there’s just a straightforward tale of heat and work.