Water intake calculator.
Find your daily hydration target. Enter your weight and how long you train, and this water intake calculator returns how much to drink - in liters and US fluid ounces - using ~33 ml per kg of bodyweight plus extra for exercise.
Total minutes of training or hard activity. Leave at 0 for a rest day.
Your daily water target
3.0 liters
about 101 US fl oz per day
Baseline
~33 ml per kg bodyweight
2.5L
Exercise add-on
~350-500 ml per 30 min
+0.6L
In glasses
roughly 250 ml each
12
A general guide, not medical advice. Food, coffee, and tea count toward the total - sip across the day and adjust for heat and sweat.
the short answer
Daily water = ~33 ml x bodyweight in kg, plus ~350-500 ml per 30 minutes of exercise. For example, a 70 kg person needs about 2.3 L baseline, and a 45-minute workout adds roughly 0.6 L - around 2.9 L, or about 98 US fl oz (1 L = 33.814 oz). It is a general guide, not medical advice.
How the water intake calculator works.
Your hydration needs scale with how big you are and how much you move. Bigger bodies hold more fluid and lose more through sweat and breathing, so a per-kilogram rule is a better starting point than a flat "8 glasses a day." This calculator works in two parts - a bodyweight baseline plus an exercise add-on:
Exercise (ml) = ~420 x (exercise minutes / 30)
Daily target = baseline + exercise
The baseline uses roughly 33 ml per kg, the midpoint of the common 30-35 ml/kg range. The exercise add-on uses about 420 ml per 30 minutes - the middle of the typical 350-500 ml guideline - because training raises sweat and breathing losses. The result is then shown in liters and US fluid ounces, where 1 liter = 33.814 fl oz.
If you enter pounds, the tool converts to kilograms internally (1 lb = 0.453592 kg) before running the math, so the formula stays correct in either unit system. Remember the number is a target for total fluid: water-rich food, coffee, and tea all count, and you should still drink to thirst and lean higher in heat, humidity, or at altitude.
How coaches use a water intake target.
Hydration is one of the simplest habits to coach and one of the most overlooked. Coaches set a clear daily water target alongside calories and protein, then turn it into a trackable habit - a checkbox the client ticks each day or a number they log. Consistent hydration supports training quality, appetite control, and recovery, so it earns a place in the plan rather than being left to chance.
Doing this by hand for a full client list is where it gets tedious. A coaching platform stores each client's weight and training, sets a sensible water goal, and shows it next to their other daily habits in a branded app - so adherence shows up in their check-ins instead of being a guess. You spend your time nudging behavior, not recalculating numbers one client at a time.
Turn targets like this into daily habits for every client.
Coachway lets you set hydration, calorie, and macro goals for each client, build their meals from 1,100+ recipes with a meal planner, and track habits and check-ins in a branded client app. It is the operating system for online fitness and nutrition coaches, so you stop stitching together calculators, spreadsheets, and chat.
See how Coachway worksWater intake calculator FAQ.
How does a water intake calculator work?
A water intake calculator estimates your daily fluid target from your bodyweight and how much you exercise. It uses about 33 ml of water per kilogram of bodyweight as a baseline, then adds roughly 350-500 ml for every 30 minutes of training. Enter your weight and exercise minutes and it returns a target in liters and US fluid ounces. It is a general guide, not medical advice.
How much water should I drink a day?
A common rule of thumb is about 30-35 ml of water per kg of bodyweight, with ~33 ml/kg as the midpoint. For a 70 kg (154 lb) person that is roughly 2.3 liters, or about 78 US fl oz, before exercise. Add about 350-500 ml for each 30 minutes you train. Your real needs shift with heat, humidity, altitude, illness, and diet, so treat the number as a starting point.
Does coffee and tea count toward water intake?
Yes. Despite the old myth, moderate coffee and tea are mildly diuretic at most and still leave you net hydrated, so they count toward your daily fluid total. Water-rich foods like fruit, vegetables, soup, and yogurt also contribute. This calculator estimates total fluid needs, so you do not have to hit the whole number from plain water alone.
How much water should I drink during a workout?
A practical guideline is about 350-500 ml of water for every 30 minutes of exercise, which this calculator adds on top of your baseline. In hot or humid conditions, or for sweaty endurance sessions, lean toward the higher end and sip steadily rather than chugging. For sessions over about an hour, adding electrolytes - especially sodium - helps you absorb and retain the fluid.
Can you drink too much water?
Yes, though it is rare. Drinking very large volumes in a short window can dilute blood sodium (hyponatremia), which is dangerous - most common in endurance athletes who over-drink plain water. The fix is to spread fluid across the day, match intake roughly to thirst and sweat, and use electrolytes on long, hot sessions rather than forcing huge amounts of plain water.
Is this water intake calculator medical advice?
No. This water intake calculator gives a general estimate for healthy adults and is not medical or clinical advice. Fluid needs change with pregnancy, breastfeeding, kidney or heart conditions, certain medications, and illness. If any of those apply to you, or you are unsure, check with a doctor or registered dietitian before changing your intake.
This calculator is general information, not medical or nutrition advice. Fluid needs vary by individual - if you are pregnant or breastfeeding, have kidney or heart conditions, or take medications that affect fluid balance, talk to a qualified professional before changing your intake.
Keep going: pair this with the TDEE calculator to set your daily calories, or the macro calculator to split them into protein, carbs, and fat. For the bigger picture, read our guide to how to do nutrition coaching online.
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Open calculator ->See what Coachway can do for your coaching business
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