Clinically reviewed by Associate Professor Christopher O’Donnell, Nurse Practitioner, FACN · Founder and Clinical Director · AHPRA NMW0001453715 · Last reviewed
Most adults in the healthy weight range burn somewhere between about 7,000 and 13,000 kilojoules (kJ) a day (roughly 1,700 to 3,100 Calories), depending on body size, age, sex and how active they are. You don’t need to burn a set number: to lose weight, what matters is that your intake sits a little below what your body uses. The familiar 8,700 kJ figure is an average, not a personal target.
If you’re an Australian adult wondering how many kJ per day you need, this guide covers the official estimates for women and men by age and activity, what 8,700 kJ on food labels means, and how to read “active” kilojoules on a smartwatch. For women of a healthy weight the estimates run from about 6,900 to 9,900 kJ a day, and for men about 8,300 to 13,300 kJ.
How many calories is 8,700 kJ?
Australia measures the energy we get from food in kilojoules. One Calorie (a kilocalorie) equals 4.184 kJ, which healthdirect rounds to 4.2.
- To turn kilojoules into Calories, divide by 4.184. 8,700 kJ is about 2,080 Calories
- To turn Calories into kilojoules, multiply by 4.184. 1,500 Calories is about 6,280 kJ
The 8,700 kJ figure is what healthdirect describes as the needs of an average adult, and it is the reference behind the “percentage daily intake” shown on many food labels. It is only a guide. Smaller, older or less active people often need fewer kilojoules. Taller, younger or more active people often need more kilojoules.
Where do your daily kilojoules go?
The total number of kilojoules you burn each day, your total daily energy expenditure (TDEE), has four main parts.
- Basal metabolic rate (BMR). The energy needed to keep you alive at rest: breathing, blood circulation, temperature control and brain function. It makes up about 45–70% of daily expenditure and rises with body size and muscle mass, which is one reason muscle matters for metabolism.
- Thermic effect of food. Digesting and storing food accounts for roughly 10% of daily energy use on a mixed diet (5–15% depending on what you eat), and protein costs more to process than fat.
- Exercise. Planned activity such as walking, swimming or the gym. A 30-minute brisk walk uses roughly 600–900 kJ for adults weighing 60–90 kg, and about a fifth of that would have been used at rest anyway.
- Non-exercise activity thermogenesis (NEAT). Everything else: standing, walking around the house, housework, gardening and fidgeting. NEAT varies a lot between people of similar size and tends to fall when you eat less, often without you noticing.
Many factors influence the total, so needs vary depending on body size, muscle mass, age, sex and activity levels. Men generally need more kilojoules than women, mainly because bigger bodies use more energy.
How many kJ per day do you need? Daily energy requirements by age and sex
Australia’s Nutrient Reference Values (NRVs) estimate how much energy adults need each day by multiplying BMR by a physical activity level. The figures below are for adults of a healthy body weight (BMI 22), rounded to the nearest 100 kJ.
| Age | Woman, 1.6 m, 56 kg: sedentary / light / moderate | Man, 1.8 m, 71 kg: sedentary / light / moderate |
|---|---|---|
| 19–30 | 7,700 / 8,800 / 9,900 kJ | 10,300 / 11,800 / 13,300 kJ |
| 31–50 | 7,600 / 8,700 / 9,800 kJ | 9,900 / 11,300 / 12,700 kJ |
| 51–70 | 7,300 / 8,300 / 9,300 kJ | 9,100 / 10,400 / 11,700 kJ |
| Over 70 | 6,900 / 7,800 / 8,800 kJ | 8,300 / 9,500 / 10,700 kJ |
How many kJ per day for a woman?
For a woman of healthy weight and about 1.6 m tall, the NRVs estimate roughly 7,600–9,900 kJ a day (about 1,800–2,350 Calories) from 19 to 50, depending on activity, and about 6,900–9,300 kJ (about 1,650–2,200 Calories) from 51. Many women need less than the 8,700 kJ average.
How many kJ per day for a man?
For a man of healthy weight and about 1.8 m tall, the estimates are roughly 9,900–13,300 kJ a day (about 2,350–3,200 Calories) from 19 to 50, and about 8,300–11,700 kJ (about 2,000–2,800 Calories) from 51.
What do sedentary, lightly active and moderately active mean?
In NRV terms, sedentary means mostly seated work, such as an office worker, with little active leisure. Lightly active means seated work with some walking and standing. Moderately active means work spent predominantly standing or walking. Regular sport of 30–60 minutes, four or five times a week, adds roughly another 1,500–2,200 kJ a day on these estimates.
Treat these as just a starting point. The NRVs note that needs can differ widely even between people of the same age, sex and size, and people in larger bodies generally use more energy than the table shows. For personalised advice, talk to a health professional (see below).
So how many kilojoules should you burn to lose or maintain weight?
There is no single number of kilojoules to aim for. Weight changes when energy in and energy out differ: if your energy intake is regularly higher than what your body burns, the extra energy is stored and you gain weight, and if it is lower, you lose weight. So the practical question is how to create a modest, sustainable gap. Energy balance is only part of the picture, as our guide to why calories in, calories out is incomplete explains.
Some practical ways to use these figures:
- Use the table, or the Eat for Health energy calculator, as a rough estimate of how many kilojoules you need to maintain your current weight
- Track your weekly average weight for three to four weeks to see whether that estimate holds for you
- Shave kilojoules mainly from food and drinks you won’t miss, since exercise alone rarely covers a large gap
- Build activity into the whole day. Australia’s movement guidelines suggest at least 30 minutes of moderate-to-vigorous activity on most days, muscle-strengthening on two or more days, and several hours of light activity
- Keep or build muscle through resistance training, which helps limit the fall in BMR as you lose fat
- Expect expenditure to fall as your weight falls, and recalculate rather than cutting further. Our article on weight loss plateaus covers why
How many active kilojoules should I burn a day?
Fitness watches and phone apps usually split your day into resting energy and active energy. Active kilojoules are only the energy you use above resting: exercise plus everyday movement such as walking, standing and housework. Your total for the day is resting and active added together.
There is no official target for active kilojoules. As a rough guide from the walking figures above, 2,000 active kJ (about 480 Calories) is about what a 60–90 kg adult would use in one and a half to two hours of brisk walking, or in a shorter workout plus a day with plenty of incidental movement. That is a solid level of activity for most adults. Whether it leads to weight loss still depends on what you eat.
Treat the numbers on your wrist as estimates. In a Stanford study that tested seven wrist-worn devices against laboratory measurement, no device estimated energy expenditure to within 20%. The kilojoule count on your watch is most useful for following your own trend from week to week, not for deciding how many extra kilojoules to eat.
When to seek review
Estimates are less reliable if you are pregnant or breastfeeding, have a medical condition such as diabetes, thyroid disease or heart failure, take medicines that affect appetite or weight, or have a history of disordered eating. Advice is also worthwhile if you are eating very little without losing weight, or feel constantly tired or hungry.
A GP, nurse practitioner or Accredited Practising Dietitian can estimate your needs more precisely and set a target that suits your health. Our nurse practitioners and dietitians can help you work out a realistic plan. Get in touch.
Frequently asked questions
Is 8,700 kJ a day right for me?
Possibly not, as it is an average adult figure. Many women and older adults need less, and many men and active people need more.
Is 10,000 kJ a day too much?
Not for everyone. On the NRV estimates it is close to the needs of a moderately active woman aged 19–30 or a lightly active man aged 51–70, but well above what a sedentary woman needs.
How many kilojoules does my body burn at rest?
For most adults of a healthy weight, BMR is roughly 5,000–7,500 kJ a day. It is higher in larger and more muscular bodies, and gradually lower with age.
How do I work out how many kilojoules I need to maintain my weight?
Start with the NRV table or the Eat for Health calculator, then check it against your weekly average weight over three to four weeks. If your weight holds steady, that is your maintenance level.
How many kilojoules are in a Calorie?
One Calorie (kilocalorie) is 4.184 kJ. Multiply Calories by 4.184 to get kilojoules, or divide kilojoules by 4.184 to get Calories.
How many kilojoules does walking burn?
A 30-minute brisk walk uses roughly 600–900 kJ for adults weighing 60–90 kg. Heavier people and faster paces use more.
Do I need to burn more than I eat to lose weight?
Yes, over time your total energy use needs to exceed your intake. That gap can come from eating a little less, moving more, or both.
How many kilojoules should I burn a day to lose weight?
There is no set number to burn. What matters is the gap between what you use and what you eat. A gap of about 2,000 kJ a day (roughly 500 Calories) would lead to around 0.4–0.5 kg of loss a week at first, slowing over time as your body adapts.
Is burning 2,000 kJ a day good?
If you mean 2,000 active kJ on a watch, yes, that is a solid amount of daily movement for most adults. If you mean 2,000 kJ in total, that is well below what your body uses just at rest, since most adults use 7,000–13,000 kJ a day in total.
References
- healthdirect. Kilojoules. https://www.healthdirect.gov.au/healthy-living/food-and-nutrition/kilojoules
- National Health and Medical Research Council, New Zealand Ministry of Health. Nutrient Reference Values for Australia and New Zealand: Dietary energy. https://www.eatforhealth.gov.au/nutrient-reference-values/nutrients/dietary-energy
- Australian Government Department of Health, Disability and Ageing. 24-hour movement guidelines: recommendations for adults (18 to 64 years). https://www.health.gov.au/topics/physical-activity/24-hour-movement-guidelines-for-all-australians/recommendations-for-adults-18-to-64-years
- Westerterp KR. Diet induced thermogenesis. Nutr Metab (Lond). 2004;1(1):5. https://doi.org/10.1186/1743-7075-1-5
- Levine JA. Non-exercise activity thermogenesis (NEAT). Best Pract Res Clin Endocrinol Metab. 2002;16(4):679–702. https://doi.org/10.1053/beem.2002.0227
- Herrmann SD, Willis EA, Ainsworth BE, et al. 2024 Adult Compendium of Physical Activities: a third update of the energy costs of human activities. J Sport Health Sci. 2024;13(1):6–12. https://doi.org/10.1016/j.jshs.2023.10.010
- Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. J Pers Med. 2017;7(2):3. https://pmc.ncbi.nlm.nih.gov/articles/PMC5491979/