Enter calories (kcal) or weight change (kg) to convert to the other using an energy-per-kg factor, with optional kJ input.
Assumptions Assumptions
- Simple energy balance model: weight change = energy (kcal) ÷ selected kcal/kg factor; no metabolic adaptation, glycogen/water shifts, or time dynamics are modeled.
- Energy is net (intake minus expenditure); positive energy implies weight gain, negative energy implies weight loss.
- Default factor 7700 kcal/kg approximates the energy content of body fat; 7500–8500 kcal/kg are common alternatives.
- Unit conversion used: 1 kcal = 4.184 kJ.
- Results are estimates and not medical or dietary advice.
When to Use This Calculator
- Estimating weight change from a known calorie surplus or deficit.
- Converting a target weight change into an equivalent energy budget.
- Sanity-checking long-term plans using a fixed kcal/kg assumption.
Input Definitions
- Energy — net energy in kcal (Cal) or kJ; the calculator converts kJ to kcal internally using 1 kcal = 4.184 kJ.
- Weight Change — change in body mass (kg); positive for gain, negative for loss.
- Energy per kg factor (F) — kcal required per kg of mass change; typical choices are 7700 (body fat), 7500 (rule of thumb), or 8500 (adipose tissue).
- Conversions — kg = kcal ÷ F; kcal = kg × F; kJ = kcal × 4.184; kcal = kJ ÷ 4.184.
- All Unit Converters
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Cal to Kg Formula
The following formulas convert energy to weight change and back using a constant energy-per-kg factor F expressed in kcal per kg.
\Delta \mathrm{kg} = \frac{E_{\mathrm{kcal}}}{F_{\mathrm{kcal/kg}}}E_{\mathrm{kcal}} = F_{\mathrm{kcal/kg}}\,\Delta \mathrm{kg}- Default factor F = 7700 kcal/kg (approximate energy content of body fat).
- Other common factors: 7500 kcal/kg (rule of thumb), 8500 kcal/kg (adipose tissue).
- 1 kcal = 4.184 kJ (so Ekcal = EkJ ÷ 4.184, and EkJ = Ekcal × 4.184).
- Sign convention: positive energy → weight gain; negative energy → weight loss.
How do you convert calories to kilograms? Divide energy in kcal by the chosen kcal/kg factor (if energy is in kJ, first divide by 4.184 to get kcal).
How do you convert kilograms to calories? Multiply the desired kg change by the kcal/kg factor (multiply by 4.184 to express the result in kJ).
Cal to Kg Conversion Table
| Energy (kcal) | Weight Change (kg) |
|---|---|
| 250 | 0.032 |
| 500 | 0.065 |
| 750 | 0.097 |
| 1,000 | 0.130 |
| 1,500 | 0.195 |
| 2,000 | 0.260 |
| 2,500 | 0.325 |
| 3,000 | 0.390 |
| 3,500 | 0.455 |
| 4,000 | 0.519 |
| 5,000 | 0.649 |
| 7,500 | 0.974 |
| 7,700 | 1.000 |
| 10,000 | 1.299 |
| 15,400 | 2.000 |
| 23,100 | 3.000 |
| 30,800 | 4.000 |
| 38,500 | 5.000 |
| * Using constant factor F = 7700 kcal/kg. Sign convention: +kcal → +kg (gain), −kcal → −kg (loss). | |
Example Problem
Convert 3,500 kcal to kilograms using F = 7700 kcal/kg.
Use the formula: Δkg = Ekcal ÷ F.
Δkg = 3500 ÷ 7700 = 0.455 kg
