Example 1
- Weight: 70 kg
- Time: 60 min
350 ml
Hydration during exercise: 70 kg × 60 min → 350 ml (5 ml/kg/h).
Hydration during exercise
Enter session time and either weight (5 ml/kg/h teaching mode) or your own sweat rate in ml/h. At 70 kg and 60 min the result is 350 ml. At 800 ml/h and 90 min it is 1200 ml. Session add-on only — separate from daily water requirement.
Result
Enter time plus weight or sweat rate. The result appears here.
The calculator computes milliliters: mass in kilograms × 5 × (minutes / 60), then rounded. It is not an individualized sweat rate and does not replace medical advice. A rough daily milliliter estimate is on the water requirement page. The same day in glasses: how many glasses of water a day.
How the result is calculated
Mass70 kg
Time60 min
Rate5 ml/kg/h
Add-on350 ml
Hydration during exercise on this page uses a teaching session rate of 5 ml per kilogram of body mass per hour. Mass is first in kilograms. Then milliliters = mass × 5 × (minutes / 60), rounded. At 70 kg and 60 min: 70 × 5 × 1 = 350 ml. At 80 kg and 90 min: 80 × 5 × 1.5 = 600 ml. At 60 kg and 30 min: 60 × 5 × 0.5 = 150 ml.
The 5 ml/kg/h figure is a teaching model on this page, not an individualized sweat rate and not an ACSM prescription. ACSM discusses general exercise fluid guidance. WHO and national nutrition education sources provide public-health hydration context. This page keeps one fixed number so the equation stays readable.
With US header units you enter pounds. The calculator converts them to kilograms before multiplying by 5. Time is always minutes. The 350, 600, and 150 ml examples are computed from kilograms. The primary result is milliliters; liters appear only as an equivalent in the result panel.
Enter weight and minutes, then Calculate. Zero minutes or an empty required value does not produce a session result. A decimal in 70.5 works: 70.5 × 5 × 1 = 352.5, and the calculator rounds to 353 ml.
This is an exercise-session add-on, not water for the whole day. A day at 33 ml/kg lives on water requirement: 70 kg with no training is 2310 ml. Heat, humidity, and illness change losses — then a clinician or coach, not the constant 5 alone.
Article hook: the same runner at 70 kg and one hour gets 350 ml from the teaching 5, but after a weigh-in loses 800 ml/h — sweat mode at 90 min then yields 1200 ml. Do not mix that with daily liters from the water-requirement page.
How to use
- Enter weight, for example 70 kg. With US units that field is pounds.
- Enter training minutes, for example 60.
- Click Calculate. 70 kg and 60 min give 350 ml.
- 80 kg and 90 min give 600 ml. 60 kg and 30 min give 150 ml.
- Water for the whole day lives on water requirement. Here only the session add-on remains.
Formula
Teaching mode: ml = round(kg × 5 × (min / 60))
Sweat mode: ml = round(rate[ml/h] × (min / 60))
Separate from 33 ml/kg per day. ACSM gives fluid context, not authorship of the constant 5.
5 ml/kg/h and the session add-on
The calculator multiplies mass in kilograms by 5 and by time in hours, then rounds milliliters. 70 kg and 60 min give 350 ml; 80 kg and 90 min give 600 ml.
- 5 ml/kg/h
- Teaching session rate on this page. An hour at 70 kg is 350 ml. This is not 33 ml/kg from the day card and not individualized sweat loss.
- ml
- Milliliters of session add-on after rounding. The primary result is ml, not liters on the main label.
- session
- Time in minutes. 90 min at 80 kg gives 600 ml. 30 min at 60 kg gives 150 ml.
- ACSM
- American College of Sports Medicine — a source of general exercise fluid guidance. It is not the author of the constant 5 on this page.
Examples
Three number sets from the same formula. Weight units in the examples follow the header.
Example 2
- Weight: 80 kg
- Time: 90 min
600 ml
Session hydration: 80 kg × 90 min → 600 ml.
Example 3
- Weight: 60 kg
- Time: 30 min
150 ml
Session hydration: 60 kg × 30 min → 150 ml.
Related calculators
FAQ
What is a hydration during exercise calculator?
It estimates a session fluid add-on: either mass × 5 ml/kg/h × hours, or your sweat rate in ml/h × hours. It is not daily water requirement and not all-day glasses.
How much water should I drink during exercise?
This page estimates milliliters for one session. Teaching mode: kg × 5 × (minutes/60) — at 70 kg and 60 min that is 350 ml. Sweat mode uses your ml/h × hours. Heat and illness need clinical judgment.
How to calculate sweat rate?
Weigh yourself before and after a session in dry clothes, add fluids drunk, convert the loss to ml per hour, then enter that rate here. The calculator multiplies ml/h by session hours.
What is a sweat rate calculator on this page?
Sweat mode multiplies the ml/h you enter by session duration. At 800 ml/h and 90 minutes: 800 × 1.5 = 1200 ml before the climate multiplier. Teaching mode still uses the fixed 5 ml/kg/h model.
What modes does this calculator have?
Two. Teaching mode: ml = kg × 5 × (minutes/60). Sweat mode: ml = ml/h × (minutes/60). At 70 kg and 60 min that is 350 ml. At 800 ml/h and 90 min that is 1200 ml.
Is this daily water requirement?
No. This page is only a session add-on. Daily ml from body mass live on the water-requirement page (e.g. 70 kg × 33 ml = 2310 ml).
How does sweat mode work?
Enter a rate in ml per hour and session minutes. The calculator multiplies rate by hours and rounds. 800 × 1.5 = 1200 ml.
Where does the 5 ml/kg/h constant come from?
It is a teaching constant in teaching mode. It is not measured sweat. In sweat mode you enter your own ml/h from a before/after weigh-in.
How do US units work?
In teaching mode weight is in pounds and converts to kilograms before × 5. Time stays in minutes. Sweat rate stays in ml/h.
Is the result medical advice?
No. Heat, humidity, and illness change losses. This is session arithmetic, not an ACSM prescription.
What does the climate choice do?
It multiplies the session add-on: cool ×0.90, temperate ×1.00, hot ×1.15, hot + humid ×1.25. It is a teaching sketch, not a body-temperature reading.
How does sweat mode differ from teaching mode?
Teaching mode: weight × 5 ml/kg/h × hours. Sweat mode: your ml/h × hours. Both split the result into before / during / after.
Is 20/50/30 an ACSM rule?
No. It is a teaching split of the same milliliter total to show three session phases.
Does the result replace daily water needs?
No. It is a training add-on. Daily water demand belongs on a separate page.
How do I measure my own sweat rate?
Weigh yourself before and after (dry clothes), add fluid drunk, convert the difference to ml/h, then enter it in sweat mode.
What about 90 minutes at 800 ml/h?
1.5 h × 800 = 1200 ml before the climate multiplier. In mild climate the result stays 1200 ml.
Does weight in pounds change the 5 constant?
No. The calculator converts pounds to kilograms; the constant stays 5 ml/kg/h.
Where is the before / during / after split?
In the result cards: about 20% before, 50% during, 30% after the same milliliter total.
Does climate also apply in sweat mode?
Yes. The climate multiplier applies to the computed total in either mode.
What unit is the session add-on in?
Milliliters for the session total, with a liter equivalent on a separate card. Climate multiplies that total.
Knowledge sources
The 5 ml/kg/h figure is a teaching model on this page. ACSM, WHO, and nutrition education sources provide fluid and hydration context, not authorship of this single number.
- ACSM — physical activity guidelines and education resources
- WHO — drinking-water fact sheet
- MedlinePlus — water in diet
- Wikipedia — drinking water
Page updated October 15, 2026.