A calculation about you, with a machine you turn yourself
Every day you make tens of kilograms of a molecule you only ever hold a handful of
The molecule is ATP. Every cell spends it to contract a muscle, fire a nerve or build a protein. At any moment your body holds about 50–100 grams of it. The rest of the story is how fast it has to be remade, and the machine that remakes it, which you can turn yourself.
A handful of ATP, spent in a few minutes
ATP is a rechargeable battery. When a cell uses it, it breaks off a phosphate group and what is left is ADP. Your mitochondria stick the phosphate back on, and the molecule is ATP again.
How often? The energy comes from food. A 2,000 kcal day means, on average, 0.41–0.55 grams of ATP remade every second. With a stock of 50–100 grams, all the ATP in you is spent and remade about once every 1.5–4 minutes.
Watch the number at the bottom. When it passes 50 grams, you will have remade as much as your body holds, on the low estimate.
The stock is an order-of-magnitude estimate: muscle holds about 5 millimoles of ATP per kilogram, and a mole of ATP weighs 507 grams.
The machine in the membrane
Food burned in the mitochondria does not make ATP directly. It pushes protons (hydrogen nuclei) across the inner membrane of the mitochondrion, like water pumped up behind a dam.
The protons flow back through one gate: ATP synthase. Its part in the membrane is a ring that turns one-eighth of a revolution for every proton that passes. In humans and other mammals the ring has eight pieces, so eight protons make one full turn.
The ring's shaft reaches up into a head about 10 nanometres across, with three sites where ADP and phosphate bind. Every third of a turn squeezes one site and out comes an ATP. Eight protons, three ATP, every turn.
The eight-piece ring was measured in cattle; the same sequence is found in every mammal studied (Watt et al., 2010).
Turn it yourself
Drag your finger or mouse across the machine, to the right. Every third of a turn, the head releases an ATP. With a keyboard: the left and right arrows.
Drag to the right to turn the machine
Turn it as fast as you can for a few seconds. Then we'll compare your finger with your body.
Turn it to the left, too. The machine also runs backwards: it splits ATP and pumps protons out. That is the direction in which it was first filmed spinning, in 1997.
Where 21,000 rpm comes from
The number gets passed around as “the speed of the turbine in your cells”. It comes from a 2005 experiment: a complete ATP synthase from Bacillus PS3, a bacterium that lives in heat, made in E. coli, stuck to a glass slide, with an 80-nanometre gold bead attached to the ring. Fed ATP at 37 °C, it turned at up to about 350 revolutions a second, or 21,000 a minute (Ueno et al., 2005).
So it was a bacterial machine running backwards: it was using ATP up. It is not even the record. The head alone of the E. coli enzyme, with smaller beads, reached bursts of 721 revolutions a second (Nakanishi-Matsui et al., 2006).
In the direction that concerns you, the one that makes ATP, the best measurement comes from membranes of beef-heart mitochondria: 420 ATP a second per enzyme, with an estimated maximum of 440 (Matsuno-Yagi and Hatefi, 1988). Divided by three ATP per turn, that is about 147 turns a second, close to 8,800 a minute. John Walker's group writes “about 100 times per second” in mitochondria, or 6,000 a minute. Nobody has yet filmed one turning inside a living human cell.
A day on the scale
On one pan, your weight. On the other, the ATP remade in a day from the food you eat.
At 2,000 kcal a day, your body remakes 36–47 kg of ATP, or 51–68% of your weight.
The range has two ends. The top assumes that all the oxygen you breathe ends up making ATP: about 32 ATP from the energy in one molecule of glucose (Hinkle, 2005). The bottom allows for the fact that, at rest, about a fifth of the oxygen your mitochondria use is lost to proton leaks that make only heat (Rolfe and Brown, 1997): about 24 ATP. That comes to 17.7–23.7 grams of ATP per kilocalorie.
The line you will find everywhere, “on any given day you turn over your body weight equivalent in ATP” (Törnroth-Horsefield and Neutze, 2008), is right as an order of magnitude. At 2,000 kcal it comes to 36–47 kg, half to two-thirds of the weight of a 70 kg adult. At 3,000 kcal, for someone doing physical work or training, it comes to 53–71 kg: their weight.
Other calculations give 57 kg a day (2,500 kcal, no leak) or 70–75 kg. The latter divide all the energy in food by the energy one ATP releases, as if every calorie ended up in ATP. Between a third and a half of it becomes heat on the way.
Put your hand on your chest
Sit still for three minutes with your palm on your chest. You will feel only your breathing. In that time your mitochondria remake roughly all the ATP you carry, with the oxygen you have just breathed in, through machines nobody will ever see turning.
Sources and method
The calculation
Energy of the day (kcal) × 17.74–23.66 g of ATP per kcal. The factor: 24–32 ATP for the energy in one molecule of glucose (686 kcal/mol), times the molar mass of ATP, 507.18 g/mol. The low figure takes off a fifth for proton leak (Rolfe and Brown, 1997); the high one uses P/O ratios of 2.5 and 1.5 (Hinkle, 2005). The counter at the bottom runs at your day's average, not the resting rate. The 50–100 gram stock is an estimate: about 5 millimoles of ATP per kilogram of tissue. The comparison with your finger: ATP per second in the whole body, divided by three ATP per turn times your turns per second; world population 8.2 billion (UN, 2024).
Sources
- Törnroth-Horsefield S, Neutze R (2008). Opening and closing the metabolite gate. PNAS 105:19565–19566. doi.org/10.1073/pnas.0810654106
- Hinkle PC (2005). P/O ratios of mitochondrial oxidative phosphorylation. Biochim Biophys Acta 1706:1–11. doi.org/10.1016/j.bbabio.2004.09.004
- Rolfe DFS, Brown GC (1997). Cellular energy utilization and molecular origin of standard metabolic rate in mammals. Physiol Rev 77:731–758. doi.org/10.1152/physrev.1997.77.3.731
- Watt IN, Montgomery MG, Runswick MJ, Leslie AGW, Walker JE (2010). Bioenergetic cost of making an adenosine triphosphate molecule in animal mitochondria. PNAS 107:16823–16827. doi.org/10.1073/pnas.1011099107
- Noji H, Yasuda R, Yoshida M, Kinosita K (1997). Direct observation of the rotation of F1-ATPase. Nature 386:299–302. doi.org/10.1038/386299a0
- Ueno H, Suzuki T, Kinosita K, Yoshida M (2005). ATP-driven stepwise rotation of FoF1-ATP synthase. PNAS 102:1333–1338. doi.org/10.1073/pnas.0407857102
- Nakanishi-Matsui M et al. (2006). Stochastic high-speed rotation of Escherichia coli ATP synthase F1 sector. J Biol Chem 281:4126–4131. doi.org/10.1074/jbc.M510090200
- Matsuno-Yagi A, Hatefi Y (1988). Estimation of the turnover number of bovine heart F0F1 complexes for ATP synthesis. Biochemistry 27:335–340. doi.org/10.1021/bi00401a050
Updated 27 September 2026