Calculate Exercise Sweat Loss and Rehydration Volume Deficit — Free
Drinking during a workout rarely replaces everything lost in sweat. Subtract in-session fluid intake from gross sweat loss and apply your post-session replacement factor to see the recovery volume still owed.
The proof surface
Training-load tools cap weekly repetition increases. This calculates post-exercise fluid replacement in millilitres from measured session sweat loss and fluid consumed during the session.
Why the flat version breaks
Replacing only 100 percent after heavy losses
Ongoing fluid excretion during recovery means one-for-one replacement leaves a lingering deficit.
Ignoring in-session bottle remainders
Count only the fluid swallowed, not what stayed in the bottle or spilled.
Treating water volume as electrolyte advice
Large sweat losses involve sodium as well as water; volume arithmetic alone does not specify electrolyte concentration.
How to work the hydration loss gauge
Convert pre- to post-exercise body-mass change (one gram equals roughly one millilitre) plus fluid drunk, or enter your logged sweat loss in millilitres.
Record the millilitres actually consumed while training. A 1,400 ml sweat loss with 500 ml drunk leaves a 900 ml net session deficit.
Sports hydration protocols commonly replace 125 to 150 percent of net deficit over recovery to account for ongoing urine losses. At 125 percent, a 900 ml deficit requires 1,125 ml of post-session fluid.
The tool flags any session where unreplaced sweat loss reaches 1,000 ml or more so you can increase in-session drinking rather than trying to chug large volumes afterward.
What the hydration loss gauge replaces
| Question | Before | Visible working |
|---|---|---|
| Replacing only 100 percent after heavy losses | Ongoing fluid excretion during recovery means one-for-one replacement leaves a lingering deficit. | Subtract fluid drunk during the workout |
| Ignoring in-session bottle remainders | Count only the fluid swallowed, not what stayed in the bottle or spilled. | Apply the post-session replacement percentage |
| Treating water volume as electrolyte advice | Large sweat losses involve sodium as well as water; volume arithmetic alone does not specify electrolyte concentration. | Review flagged high-deficit sessions |
A local arithmetic aid replaces hand calculation, not expert review. No paid AI service is needed.
Run it on the samples, right here
FIRST-LOAD
Input is processed locally and a draft is saved automatically in this browser profile when storage is available. Reset to sample clears that draft; Pro history has its own clear button. A state link encodes your inputs in its URL: share only non-sensitive rows. Browser history, clipboard and anyone receiving the link may retain it. Optional AI use below leaves this device; it is not required.
Fluid volume arithmetic from user-entered session figures. Not clinical or sports-medicine advice; consult a clinician or registered sports dietitian for heat illness, kidney conditions or sodium replacement.
Data note: Everything runs in this browser tab on the hydration loss gauge: your training session | gross sweat loss ml | fluid drunk during session ml stays on this device, nothing is uploaded, and the reading is rebuilt only when you press run.
Go deeper: the companion app files the same reading as a meter band gauge
The article demo above runs without limits. The companion app keeps a local history, exports the rows as CSV, prints the hydration loss gauge reading, and holds your drafts on this device — one free run, then $ 4 one-time for the layer that keeps filing.
The hydration loss gauge reading is complete for free. The optional $4 layer adds print, row CSV and the last five local reading summaries; it does not add hidden answers. Checkout is not configured yet; the article demo remains unlimited.
Open the calculate exercise sweat loss and rehydration volume deficit companionBoundary
Fluid volume arithmetic from user-entered session figures. Not clinical or sports-medicine advice; consult a clinician or registered sports dietitian for heat illness, kidney conditions or sodium replacement.
What this is built on
- Method: Sports hydration protocols commonly replace 125 to 150 percent of net deficit over recovery to account for ongoing urine losses. At 125 percent, a 900 ml deficit requires 1,125 ml of post-session fluid.
- All sample records are invented examples. The app does not fetch measurements, policies, files or personal records.
- Google’s official pricing page, fetched 2026-09-29, lists free-tier access including AI Studio. Optional formatting only; limits and availability can change. Free-tier content may be used to improve products. Never paste private records there.
Before: Ongoing fluid excretion during recovery means one-for-one replacement leaves a lingering deficit. After: the hydration loss gauge shows the working beside each named row so the reader can change the assumption and inspect the consequence.
Optional AI formatting, not calculation
For this hydration loss gauge, use the free AI Studio interface only if available to you, with no paid API key. Manual entry completes the same workflow for free. Supply only fictional or non-sensitive notes. Review its output against the source; never paste unresolved questions into the numeric rows.
Format my non-sensitive notes for a hydration loss gauge. Return plain rows only: training session | gross sweat loss ml | fluid drunk during session ml. Preserve supplied quantities exactly. Do not guess missing values; list questions separately. Do not calculate or add advice. I will check every row before pasting into the local tool.
Accepted schema: training session | gross sweat loss ml | fluid drunk during session ml. No AI response is executed as code.