Quick answer: sports nutrition guidelines suggest drinking about 5 to 10 mL per kg of body weight in the 2 to 4 hours before exercise. For a 75 kg person that's roughly 375 to 750 mL, spread out rather than gulped. Aim for pale straw coloured urine, and if it's still dark, have a little more around 2 hours before you start.
"Drink plenty of water" isn't much help when you're trying to work out what to have before a 6am class or an afternoon run. Here's a simple, science-based timing guide for drinking before exercise.
The guideline in plain English
The 2016 joint position from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine recommends drinking 5 to 10 mL per kg of body weight in the 2 to 4 hours before exercise. ACSM's fluid replacement position stand gives a similar plan: about 5 to 7 mL per kg at least 4 hours before, then another 3 to 5 mL per kg about 2 hours before if you're not passing urine or it's dark.
Drinking early gives your body time to absorb what it needs and pass any excess before you start, so you're not running to the toilet mid-session.
Your pre-exercise drink chart
| Body weight | 2 to 4 hours before (5 to 10 mL/kg) |
|---|---|
| 55 kg | 275 to 550 mL |
| 65 kg | 325 to 650 mL |
| 75 kg | 375 to 750 mL |
| 85 kg | 425 to 850 mL |
| 95 kg | 475 to 950 mL |
Use the lower end for short sessions in mild weather, and the higher end for long, hot or very sweaty sessions.
Early morning sessions
You can't drink 4 hours before a 6am workout without an alarm at 2am. Instead:
- Drink normally through the evening before.
- Have a glass of water as soon as you wake.
- Sip a further drink on the way, finishing about 20 to 30 minutes before you start. The International Society of Sports Nutrition gives an example of 400 to 600 mL in the 20 to 30 minutes before exercise.
Does sodium help before exercise?
ACSM notes that sodium-containing drinks or salty snacks help stimulate thirst and help the body retain the fluid you drink. For most people, a normal meal with some salt does the job. On hot days or before long sessions, a drink containing sodium is an easy option. Large "sodium loading" protocols used by some elite endurance athletes are a different thing and best done with a sports dietitian.
Can you drink too much?
Yes. More isn't always better. The US National Athletic Trainers' Association says recreational exercisers shouldn't need extra fluid beyond normal before activity, and drinking far beyond your needs brings no advantage. The goal is to start hydrated, not overloaded. If you're drinking so much you feel sloshy or keep needing the toilet, ease off.
Signs you're starting behind
- Dark yellow urine, or not needing to go for hours
- Thirst or a dry mouth before you even start
- A headache or feeling flat
- A big session yesterday, a hot night or a few drinks the evening before
Make the before easy.
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Read next: why starting hydrated matters, according to the science and the best time to drink electrolytes.
Frequently asked questions
How much water should I drink before a workout?
About 5 to 10 mL per kg of body weight in the 2 to 4 hours before, which is roughly 375 to 750 mL for a 75 kg person.
How long before exercise should I stop drinking?
You don't need to stop, but finishing your main drink 20 to 30 minutes before you start helps avoid an uncomfortably full stomach.
What should I drink before a morning workout?
A glass of water when you wake, then another drink on the way. Add some sodium if it's hot or a long session.
Is it bad to drink a lot of water right before exercise?
Big volumes right before can feel uncomfortable and won't be absorbed in time. Spreading your drinks over the hours before works better.
Sources: Thomas, Erdman & Burke, J Acad Nutr Diet 2016; Sawka et al., ACSM position stand, Med Sci Sports Exerc 2007; Kerksick et al., J Int Soc Sports Nutr 2018; McDermott et al., NATA position statement, J Athl Train 2017; Sports Dietitians Australia, Fluids in Sport. General information only, not medical advice. If you have a health condition, check with your doctor.
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