Energy Converter

Type a number, pick the unit you're starting from, and every other energy unit fills in at once, live, updating as you type. Joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, electronvolts, and foot-pounds, all sitting there together. Most energy converters won't do that. They make you pick a from unit and a to unit and give back one answer, so checking a food label in kcal against your power bill in kWh against an air-conditioner spec in BTU means running the same conversion three separate times, re-choosing the target box on every round. Here you set your source once and read the rest straight off the table.

Every row has its own copy button, so grabbing a value doesn't mean dragging your cursor across a run of digits. And if you want to hand someone the exact conversion, Copy shareable link drops your value and unit into the web address, they open the page already filled in. All of it runs in your browser, nothing you type is uploaded, and once the page has loaded it keeps converting with no connection at all.

1. Type your value in the Value box. A whole number, a decimal, or scientific notation like 1.5e6 all work fine.
2. Pick your starting unit in the From dropdown. That's the only unit you have to choose, the rest are calculated for you.
3. Read the answer off the table. Every unit shows its converted value and updates the instant you type. Your source unit's row is highlighted so you don't lose track of which one you picked.
4. Copy a single value with the copy button on its row. Handy when you only want the one number and want it clean.
5. Copy shareable link to send the exact conversion to someone else. The link carries your value and unit, so the page opens pre-filled on their end.

Every factor built in is the standardized one, and results carry eight significant figures, plenty for engineering or schoolwork.

If energy units bite anyone, it's here. A calorie with a lowercase c (cal) is tiny, about 4.184 joules, the heat it takes to warm one gram of water by one degree Celsius. A Calorie with a capital C, the one printed on every food label, is a thousand of those, which makes it a kilocalorie, or 4,184 joules. Labels almost always mean the big one even when they print the little c, which is precisely how people end up mixing the two.

So a candy bar that says 250 calories really holds 250 kilocalories, about 1,046,000 joules. Read it as small calories and you'd be off by a factor of a thousand.

This tool lists cal and kcal as separate rows on purpose, so you never have to guess which one a source meant. A nutrition label wants kcal, and a chemistry problem that says calories almost always means the small cal. Not sure which you're holding, check the size, food energy lands in the hundreds or low thousands of kcal and never the millions. (The tool uses the thermochemical calorie, 4.184 J, the one nutrition science uses. A slightly larger definition, 4.1868 J, shows up elsewhere, but the gap is under a tenth of a percent and never matters here.)

Your electricity meter counts kilowatt-hours, and it pays to know what one is. A kilowatt-hour is what a 1,000-watt appliance uses in an hour. Run a 1,500-watt space heater for an hour and that's 1.5 kWh. Leave a 60-watt bulb on all day and you've used about 1.44 kWh (60 watts times 24 hours). Multiply your total kWh by your rate and you have the cost, so if your utility charges 15 cents per kWh and you burned 900 kWh, that's $135.

In joules a single kWh is 3,600,000 (1,000 watts times 3,600 seconds), which is why nobody bills in joules, the invoices would run to millions of digits. One kWh is roughly 860 food Calories, so the energy your fridge pulls in a couple of hours is about the energy in your lunch.

Watt-hours (Wh) are the same idea a thousand times smaller, which is why batteries use them. A phone battery holds maybe 15 Wh, an electric-car battery runs 60,000 to 100,000 Wh, or 60 to 100 kWh.

The joule (J) is the SI base unit, and every other unit here is just some number of joules. It's small (lifting a small apple one meter costs about one), which is why the everyday units are all big multiples of it. The BTU is worth a real warning: an "8,000 BTU" air conditioner almost always means 8,000 BTU per hour, a rate, not a fixed amount of energy, and this tool converts BTU as an energy quantity (one BTU is 1,055.0559 joules). At the tiny end, the electronvolt (eV) is about 1.602e-19 joules, the energy an electron picks up crossing a one-volt gap, which is what physics and chemistry use for photons and chemical bonds. And foot-pounds (ft·lb) are about 1.356 joules each. Careful with that one. Torque is quoted in pound-feet, which works out to the same number and measures something else entirely, so check that your source means energy before you convert it. The row here is the energy unit.

Rounding is display only. The math runs at full precision and the tool just trims how many digits it shows, so a clean 860.4 on screen still sits on an exact value underneath. Very large and very small results flip to scientific notation on their own, so one joule in electronvolts reads as something like 6.24e+18 instead of eighteen digits nobody can read.

Negative values convert fine, but they're usually a signal to double-check. Energy is almost always positive, so a stray minus sign is usually a typo. The tool will flip the sign and convert it, it won't stop you, so if you didn't mean it that's your cue to look again.