Before anything else on this page: drinking too much plain water during prolonged exercise can kill you. The condition is exercise-associated hyponatremia, and it happens when fluid intake dilutes blood sodium faster than the body can excrete the excess water. The StatPearls chapter on exercise-associated hyponatremia published on the NCBI Bookshelf describes how excessive intake of hypotonic fluid, combined with exercise-driven antidiuretic hormone secretion, raises total body water relative to total body sodium, and how the severe form — hyponatremic encephalopathy, presenting as altered mental status, seizure and coma from cerebral oedema — is often fatal. Deaths at marathons and endurance events have been attributed to it. It is not a rare curiosity; it is the reason "drink as much as you can" stopped being sound guidance.
Arb Digital publishes free sport and business calculators, and this one has a deliberately narrow job. It converts a bottle size and a stated concentration into the grams of sugar and salt that produce that concentration. It does not tell you how much to drink, when to drink it, or what concentration is right for you, because those questions depend on your sweat rate, your sweat sodium, the weather, the event and your own physiology — and the published default guidance for most people is to drink according to thirst.
What This Sports Drink Calculator Does
You give it a volume and two target concentrations: carbohydrate as a percentage weight in volume, and sodium in millimoles per litre. It returns the mass of carbohydrate to dissolve, the mass of salt to add, the resulting sodium content of the bottle in milligrams, the sodium concentration per litre in milligrams, and the energy the carbohydrate contributes. The salt figure adjusts for the sodium fraction of whatever salt you are using, which matters because salt substitutes and blends are not all 39.34% sodium by mass the way pure sodium chloride is.
What it does not do is set an intake, produce a verdict, or judge the concentrations you enter. There is no green tick for a "good" mix and no warning for a "bad" one, because those judgements belong to a sports dietitian or clinician who knows you and can measure things this page cannot see.
How to Use It
- Enter the volume of the bottle you are mixing and pick the unit. This is a container size, not a target intake.
- Set the carbohydrate concentration as a percentage weight in volume. Read the published ranges below before choosing one.
- Set the sodium concentration in millimoles per litre, or convert from a milligrams-per-litre figure using the relation in the formula section.
- Adjust the sodium fraction of your salt if you are not using plain sodium chloride.
- Weigh the resulting masses on a kitchen scale rather than converting them to spoons.
The Formula and How It Is Calculated
Carbohydrate mass is the simplest part: percentage weight in volume means grams per 100 millilitres, so carbohydrate (g) = volume (ml) × concentration (%) ÷ 100. A 750 ml bottle at 6% needs 45 g. Energy follows by multiplying that mass by the energy factor, conventionally 4 kcal per gram for carbohydrate, which is why the factor is an editable input rather than a hard-coded constant.
Sodium takes one extra step because it is conventionally expressed in millimoles. Sodium has a relative atomic mass of about 22.99, so 1 mmol of sodium = 22.99 mg. Multiply your target concentration in mmol per litre by the bottle volume in litres to get millimoles in the bottle, then by 22.99 for milligrams of sodium. To get the mass of salt, divide that sodium mass by the sodium fraction of the salt: for pure sodium chloride, 39.34% by mass, so salt (mg) = sodium (mg) ÷ 0.3934. A 750 ml bottle at 25 mmol per litre therefore contains 18.75 mmol, about 431 mg of sodium, requiring roughly 1.10 g of table salt.
The Published Ranges, and Why They Are Ranges
Commercial isotonic sports drinks are typically formulated with carbohydrate in the region of 4 to 8 per cent and sodium in the region of 20 to 30 millimoles per litre. The American College of Sports Medicine position stand on exercise and fluid replacement discusses the inclusion of sodium at 0.5 to 0.7 grams per litre of water for exercise lasting longer than an hour, noting it may help palatability and fluid retention; that band works out at roughly 22 to 30 millimoles per litre.
The carbohydrate ceiling has a physiological basis. A study in Nutrition & Metabolism on beverage glucose and sodium content and fluid delivery used deuterium tracers to measure how quickly ingested fluid reached the bloodstream and found that fluid delivery was compromised as glucose concentration rose above 6%, with a 3% drink outperforming 6% and 9% ones. That is a real trade-off rather than a rule: a more concentrated drink carries more fuel per bottle and less water per minute into circulation, and which side of that trade matters more depends entirely on the event.
These are published ranges observed across populations and products. They are not a prescription, and this page does not present them as one. Nothing here tells you which number inside those bands belongs in your bottle.
Sweat Rate and Sweat Sodium Vary Enormously
The single most important thing to understand about hydration arithmetic is how wide the individual variation is. Sweat rates during exercise differ by several-fold between people doing the same session in the same conditions, driven by body size, fitness, acclimatisation, clothing, heat and humidity. Sweat sodium concentration varies at least as much: the difference between a low-sodium sweater and a heavy salt-loser is large enough that a single drink formulation cannot serve both well.
This is why laboratory sweat testing exists and why serious endurance athletes get it done. It is also why any published concentration is a starting reference rather than an answer. If you want a figure that reflects your own physiology, the route is measurement and a sports dietitian, not a web page. Our salt to sodium converter is useful alongside a sweat test result, because laboratory reports and food labels switch between salt and sodium units constantly and the two differ by a factor of about 2.54.
Drinking to Thirst Is the Published Default
The guidance that emerged after the hyponatremia deaths of the late 1990s and 2000s is that most people exercising for most durations should drink according to thirst rather than to a schedule. Thirst is a reasonably good regulator in ordinary conditions, and drinking ahead of it — on a plan, to a bottle-per-hour target, or on the old advice to stay ahead of dehydration — is the behaviour most strongly associated with dangerous dilution of blood sodium.
Adding sodium to a drink does not make overdrinking safe. A drink at 25 mmol per litre is still substantially more dilute than blood plasma, so consuming large volumes of it can still lower blood sodium. Electrolyte content changes palatability and fluid retention; it does not license drinking more than thirst calls for. Anyone who becomes confused, disoriented, nauseated, or develops a headache during or after a long event needs medical assessment, and being given more fluid before that assessment can make hyponatremia considerably worse.
Practical Notes on Mixing
Weigh everything. A level teaspoon of fine table salt and a level teaspoon of coarse sea salt differ substantially in mass because the crystals pack differently, and a recipe expressed in spoons can be out by a third. The same applies to sugar. A cheap kitchen scale removes the whole problem.
Dissolve fully in a little warm water before topping up, especially with sucrose at the higher end of the range. Undissolved sugar sitting at the bottom of a bottle means the first mouthfuls are more dilute than intended and the last are far more concentrated. Mix fresh: a sugar solution left warm for hours is a growth medium. If you are counting the carbohydrate as part of a wider intake, the grams to calories calculator and the sugar intake calculator handle the bookkeeping. Ordinary daily fluid is a different question from exercise fluid entirely.
Arb Digital builds fast, dependency-free calculators and the content architecture that makes them rank. Browse the free library or get in touch about your own.
Browse All Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Treating the bottle volume as an intake target — it is the size of the container you are mixing, and this page sets no intake for anyone.
- Confusing salt with sodium — sodium chloride is only 39.34% sodium by mass, so a gram of salt is not a gram of sodium.
- Measuring salt by spoon — crystal size changes the mass in a level spoon dramatically, and the error goes straight into the concentration.
- Assuming electrolytes make overdrinking safe — a sports drink is still far more dilute than plasma, and large volumes can still lower blood sodium.
- Pushing carbohydrate concentration up to carry more fuel — published work shows fluid delivery slows as concentration rises above roughly 6%, so you trade water for sugar.
Related Free Tools From Arb Digital
For energy bookkeeping around long sessions there is the running calorie calculator and the cycling calorie calculator. If you are pacing an event rather than fuelling it, use the running pace calculator or the triathlon finish time calculator. Daily fluid, as opposed to exercise fluid, is covered by the water intake calculator. Everything is listed in the free online tools hub.
Frequently Asked Questions
Yes. Exercise-associated hyponatremia occurs when fluid intake dilutes blood sodium faster than the body can excrete the excess water, and the severe form, hyponatremic encephalopathy, causes cerebral oedema and is often fatal. Deaths at endurance events have been attributed to it.
This page does not answer that and cannot. The published default guidance is to drink according to thirst rather than to a schedule, and an individual plan is something a sports dietitian or clinician sets after measurement. Drinking ahead of thirst is the behaviour most strongly linked to dangerous dilution of blood sodium.
Commercial isotonic drinks are commonly formulated with carbohydrate in the 4 to 8 per cent band and sodium around 20 to 30 millimoles per litre. The ACSM position stand on exercise and fluid replacement discusses sodium at 0.5 to 0.7 grams per litre for exercise lasting over an hour. These are published ranges observed across products, not a recommendation for any individual.
Because it slows fluid delivery. A study using deuterium tracers found that fluid absorption was compromised as glucose concentration rose above roughly 6 per cent, with a 3 per cent drink outperforming 6 and 9 per cent ones. A stronger drink carries more fuel per bottle and less water per minute into circulation.
Not reliably. A drink at typical sports-drink sodium concentrations is still much more dilute than blood plasma, so drinking large volumes of it can still lower blood sodium. Sodium affects palatability and fluid retention; it does not make overdrinking safe.
Because not all salt is pure sodium chloride. Sodium chloride is 39.34 per cent sodium by mass, but low-sodium substitutes replace part of that with potassium chloride and blends vary. Entering the fraction from your packet keeps the sodium figure honest.
Because crystal size changes how much mass fits in a level spoon. Fine table salt and coarse sea salt differ substantially per spoon, and that error transfers directly into the concentration of the finished drink. A kitchen scale removes the problem.
This tool performs unit arithmetic on figures you enter and is for general information only. It is not nutrition advice, it sets no intake for anyone, and it makes no judgement about the concentrations you choose. Fluid and electrolyte needs during exercise vary enormously between individuals and conditions, and getting them wrong can be dangerous. Consult a registered sports dietitian or a physician for individual guidance, and seek immediate medical assessment for confusion, disorientation, persistent nausea or headache during or after prolonged exercise.
