Pounds to Calories Converter

A pounds to calories conversion tells you how much energy is stored in a given amount of body weight. The usual answer is 3,500 calories per pound of body fat, or about 7,700 calories per kilogram. It is a handy rule of thumb, but it is an estimate, and the sections below explain how far to trust it.

What the Conversion Measures

This tool measures the energy value of a weight change, in kilocalories (what food labels call "calories"). It does not predict how much weight you will lose or gain on a diet, because real bodies adjust as weight changes.

The Formula

Calories = Pounds x 3,500 (or Kilograms x 7,700)

Daily gap = Total calories / (Weeks x 7)

The 3,500 figure traces back to a 1958 estimate of the energy in body fat tissue¹.

How This Calculator Computes Your Result

Enter an amount in pounds or kilograms, then choose loss or gain. Pounds use 3,500 calories per pound and kilograms use 7,700 per kilogram, so the two units differ by about 0.2% because both numbers are rounded. Add a number of weeks to see the average daily deficit (for loss) or surplus (for gain) and the weekly pace. You can also enter the share of the change that is lean tissue. The tool then shows a second estimate next to the classic one. Entering 0% lean does not return the classic 3,500, because the classic rule already behaves like a mix of fat and some lean tissue (see below). Totals and daily numbers are rounded to whole calories.

The tool accepts 0.1 to 500 pounds (or 0.1 to 227 kilograms) and 1 to 520 weeks. If the daily gap is above 1,000 calories, which equals 2 pounds a week, the tool adds a note that this is a fast pace.

What Your Result Means

Here is what common amounts equal under the classic rule:

The daily number is the same total spread evenly over your weeks. For example, 10 pounds over 12 weeks works out to 35,000 / 84 days, or about 417 calories a day. That is arithmetic, not a forecast. Treat it as the most the plan could deliver on paper, because the result over time is usually smaller.

Why 3,500 Is Only a Rough Rule

Body fat tissue is not pure fat. The 3,500 rule treats every pound lost as the same mix of tissue. In practice, some of the weight you lose is lean tissue, which holds far less energy than fat. Researchers estimate about 9,440 calories per kilogram for pure fat and about 1,820 for lean mass². The more lean tissue in the mix, the fewer calories one pound is worth.

This table shows the effect, using those two values:

Pure fat is not the same as the classic rule. A change that is 100% fat works out to 4,282 calories per pound, not 3,500, because pure fat holds more energy than the tissue the classic rule describes. A mix of about 23% lean tissue gives roughly 3,500 per pound, so the classic rule fits many people who start with a lot of body fat. Hall found it matches people with more than 30 kg (66 pounds) of body fat and overstates the deficit needed for leaner people². This is why the optional lean share box can change your result.

Why Real Results Fall Short Over Time

The 3,500 rule assumes your daily deficit stays the same all the way down. It does not. As you lose weight, your body needs less energy, so the gap shrinks³. A model by Hall and colleagues shows that weight responds slowly: it takes about a year to reach half of the eventual change, and about three years to get most of the way there³. They estimate that each permanent change of about 10 calories a day leads to roughly one pound of eventual change³.

Apply that to a 500 calorie daily deficit. The 3,500 rule says you lose about 52 pounds in a year. Hall's rule of thumb points to about 46 pounds eventually, with around half of that in the first year³. Hall and Chow call the main flaw of the 3,500 rule its failure to account for these dynamic changes⁵.

Behavior matters too. A review of real-world studies found that people who diet lose up to 12 to 44% less than the rule predicts, as eating and activity shift⁴.