Example 1
- Weight: 70 kg
- Activity: none
≈ 2.31 L/day
A typical target for a day without much exercise.
Water requirement calculator
Type weight and activity. 70 kg with no add-on is 2310 ml. 60 kg plus light work is about 2.33 L. 90 kg in heat is about 3.67 L. A guide, not an order.
Weight × 33 ml plus 0, 350, or 700 ml. Heat, fever, and pregnancy change needs. Daily calories live on TDEE. Grams live on protein requirement.
Result
Weight (kg) and Activity. The result shows up here.
How results are calculated
Water need is weight [kg] × 33 ml plus an activity add-on. With a US header you type pounds; the formula still multiplies kilograms by 33 ml. 70 kg with no add-on: 70 × 33 = 2310 ml, about 2.3 L. 80 kg: 2640 ml from weight. 60 kg plus light work: 1980 + 350 = 2330 ml. 90 kg and hard work or heat: 2970 + 700 = 3670 ml.
Add-on: 0 / +350 / +700 ml (none / light under 45 min / intense or heat). The 33 ml/kg constant sits in the common 30-35 band. Tea, soup, and water in food count too, not only tap water. With a lot of caffeine some people add another glass beside it.
Type weight in the label unit and pick activity, then Calculate. A comma in 70.5 parses. 58 kg with no add-on: 58 × 33 = 1914 ml. 82 kg and hard work: 2706 + 700 = 3406 ml. Heat and humidity raise sweat loss, so take the 700 ml add-on then.
A sketch for an ordinary day. Fever, pregnancy, breastfeeding, and some kidney conditions change needs: then a doctor, not this constant. In older people thirst can fade, so dehydration is easier. TDEE and protein next door count calories and grams, not liters.
Dark urine, a dry mouth, and a headache can mean you are short. Pale yellow urine most of the day usually means you are close. Do not force liters in reserve; rare hyponatremia is possible.
Drink steadily, from thirst plus the day's context. Extra water is only after exercise.
How to use
- Type weight, for example 70 kg. With a US header that field wants pounds.
- Pick activity: none, light work under 45 minutes, or hard work or heat.
- Click Calculate. 70 kg with no add-on gives 2310 ml, about 2.3 L.
- 60 kg and light work give 1980 + 350 = 2330 ml. 90 kg in heat: 2970 + 700 = 3670 ml.
- Daily calories live on TDEE. Protein grams live on protein requirement. Here the liters stay tied to weight.
ml, 33, and the activity add-on
Weight times 33 ml, then 0, 350, or 700. 70 kg with no add-on is 2310 ml; 60 kg plus light work is 2330 ml.
- ml
- Milliliters of fluid for the day from this card. 70 × 33 = 2310 ml, about 2.3 L. A weight sketch, not a clinic order.
- exercise
- The activity add-on: light adds 350 ml, intense work or heat adds 700. 90 kg plus 700 is 3670 ml.
- hyponatremia
- Low blood sodium from flooding liters. At 58 kg the base is 1914 ml; the calculator does not ask you to pour a spare stash on top.
Usage examples
Example 2
- Weight: 60 kg
- Activity: light exercise
≈ 2.33 L/day
The extra 350 ml covers fluid lost during a shorter workout.
Example 3
- Weight: 90 kg
- Activity: intense exercise / heat
≈ 3.67 L/day
Higher weight plus intense exercise pushes the need up noticeably.
Related calculators
FAQ
How many ml at 70 kg with no add-on?
70 × 33 = 2310 ml, about 2.3 L. A start from weight. Heat or an hour of running you add separately, not inside the 33.
Must 80 kg always drink 2.6 L of plain water?
80 × 33 = 2640 ml from weight. Tea, soup, and food water count too. Pregnancy, fever, and kidneys change the need.
Where do 350 and 700 ml come from?
Light work adds 350 ml, hard work or heat adds 700. 60 kg plus 350 is 2330 ml. 90 kg plus 700 is 3670 ml.
Do coffee and tea count?
Yes, they join the fluid balance. With a lot of caffeine some people still add a glass of water beside the cup.
How do I know I am drinking too little?
Dark urine, a dry mouth, a headache. Pale yellow urine most of the day usually means you are close.
Can I overdo it?
Rarely, but hyponatremia is possible. Do not force liters in reserve. Drink steadily, by thirst plus context.
How much at 58 kg with no training?
58 × 33 = 1914 ml. At 82 kg with the intense setting: 2706 + 700 = 3406 ml.
Does climate matter?
Heat and humidity raise sweat loss. Take the 700 ml add-on, or drink more than the calculator if urine darkens.
What about older adults?
Thirst can fade, so dehydration is easier. Often you drink on a plan, not only when you feel thirsty.
Where are calories and protein?
TDEE counts daily kcal. Protein requirement counts grams from mass. Here it is only weight × 33 ml plus the add-on.
Knowledge sources
Weight × 33 ml plus an effort add-on. Heat, fever and pregnancy change needs.
Page updated in 2026.