Race day
Marathon Hydration Calculator
Quick answer
Enter the volumes you chose and confirm refill availability with the event. This checks carrying capacity; it does not prescribe how much to drink or replace all sweat loss.
Aid-station carrying plan
Enter the volumes you chose and confirm refill availability with the event. This checks carrying capacity; it does not prescribe how much to drink or replace all sweat loss.
Route edits stay in this tab. Download your route PDF before leaving; daily-calculator share links do not include this route.
Leg 1
Leg 2
The chosen plan fits your capacity.
Required carry includes all chosen amounts until the next available refill, plus reserve. Reserve is carried once; it is not added to drinking totals.
Chosen total: 0 ml · 60 min
Refill stops: 0
Leg 1
Required at start of leg: 0 ml
Unused capacity: 500 ml
Leg 2
Required at start of leg: 0 ml
Unused capacity: 500 ml
Printable planning sheets
Preview and download without an account. Personalized files are made in your browser.
PDFs are available in English and Portuguese (Brazil). The preview shows the selected file language.
Race carrying card
Your chosen plan - amounts are not a prescription
Container: 0.50 L
Reserve: 0.00 L
| Leg / minutes | Chosen use | Required carry | Capacity shortage | Refill after |
|---|---|---|---|---|
| 1 / 30 min | 0.00 L | 0.00 L | 0.00 L | Yes |
| 2 / 30 min | 0.00 L | 0.00 L | 0.00 L | No |
Required carry covers the next available refill plus reserve. A shortage means the chosen plan does not fit. Verify station availability with the event; this tool cannot guarantee access.
Adult planning tool. Clinical fluid limits and clinician instructions override this sheet. Do not force drinking to complete a target.
Daily estimates use site assumptions, not a measured need. Team and race amounts are chosen by you; no medical dose or sodium requirement is calculated.
waterdailygoal.com/methodology | waterdailygoal.com/hydration-evidence
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Daily beverage estimate (separate from the race plan)
Fine-tuneMeasure in bottles · Your day
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Your daily goal: 125 ounces, 15 glasses.
Your daily goal
Updates instantlyof water a day · about 15 glasses · 7.5 half-litre bottles
Planning scenarios: 115-142 fl oz. Use it as a flexible target, not a medical limit.
Start
2.5 glasses
7:00 AM
Taper
9:00 PM
for better sleep.
Food fluid
+0.9 L
typical food water
- 3.7
- Litres
- 125
- Ounces
- 15
- Glasses
Why this number
WaterDailyGoal uses 33 ml/kg for a beverage planning estimate. The 30–40 ml/kg scenarios and activity/climate coefficients are site assumptions, not validated personal requirements or NAM/EFSA formulas. Pregnancy, breastfeeding, and GLP-1 medicines do not automatically change this estimate. Population total-water references include food; they are not minimum drinking doses. Follow individual clinical advice.
Full methodologyNext step
Your sip schedule
- 7:00 AM · Start the day2.5 glasses
- 9:48 AM · Top up2.5 glasses
- 12:36 PM · Top up2.5 glasses
- 3:24 PM · Top up2.5 glasses
- 6:12 PM · Top up2.5 glasses
- 9:00 PM · Wind down2.3 glasses
Ease off after 9:00 PM for better sleep.
Electrolytes? Consider sweat losses
Electrolytes are not automatic. Long or heavy sweating and vomiting or diarrhea need different approaches; food, losses and medical restrictions matter. Ask a clinician or pharmacist when illness is involved.
A friendly estimate for healthy adults, not medical advice. Your needs rise with heat, exercise, illness, pregnancy, and some medications. Don't drink more than ~1 litre per hour.
Daily goal
125 fl oz
The link and preview image include your weight and settings.
Practice the plan before race day
Practice your chosen drink, carrying setup and refill timing during training. Check the event's actual stations and prepare for a missed refill. The daily estimate below is a separate site planning assumption, not an amount to add automatically to the race plan.
Use aid stations as checkpoints
Required carry includes all chosen amounts until the next available refill, plus reserve. Reserve is carried once; it is not added to drinking totals.
Frequently asked
How much should I drink during a marathon?
Enter the volumes you chose and confirm refill availability with the event. This checks carrying capacity; it does not prescribe how much to drink or replace all sweat loss.
Should I drink at every aid station?
Required carry includes all chosen amounts until the next available refill, plus reserve. Reserve is carried once; it is not added to drinking totals.
Does this calculate a sodium dose?
No. This is a carrying and refill planner for amounts you choose. It does not calculate sodium needs or prescribe full replacement of measured sweat losses. Use individual clinical or event medical guidance where appropriate.
Sources
- 1.American College of Sports Medicine, Exercise and Fluid Replacement — Athletes should start exercise euhydrated, limit body-mass losses during training, and replace fluid and sodium after heavy sweat losses.
- 2.McDermott et al., NATA Position Statement, 2017 — Sweat rate varies widely by athlete, heat, intensity, clothing, and acclimation, so pre/post body-weight checks are the practical way to individualise fluid plans.National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active; individualized replacement and overdrinking
- 3.Mayo Clinic — General guidance of roughly 2.7–3.7 L of total fluids a day, with thirst and pale-yellow urine as everyday checks.