Saltify Rehydration Calculator

Hydration calculator

Get a starting plan for before, during and after your event. Built for hot conditions.

Body weight (kg) Event duration (minutes) Intensity Heavy or salty sweater? Used to estimate sodium concentration. Ignored if you enter your own sweat sodium below.

I know my sweat rate

Sweat rate (L/hour) Weigh yourself nude before and after a 1-hour session, and add any fluid you drank. Each kg lost is about 1 L of sweat. Leave unticked to use the average estimate.

I know my sweat sodium concentration

Sweat sodium (g/L) Sodium, not salt (1 g sodium is about 2.5 g salt). Typical range is 0.2–2.0 g/L, average about 0.9. Comes from a sweat patch or lab test. Leave unticked to use the average estimate.

Assumptions (high heat)

Air temperature around 30–35°C, humidity 60% or higher, limited shade.
Typical sweat rate: 0.7 L/h easy, 1.0 L/h moderate, 1.4 L/h hard, for a 70 kg athlete, scaled by body weight.
Sweat sodium concentration around 0.9 g/L (the real range is wide, roughly 0.2–2.0 g/L). Heavy salty sweaters are estimated at 1.5 g/L and light sweaters at 0.6 g/L.
You are reasonably heat-acclimatised. If not, expect higher sweat and sodium loss.

Country/region

Hydration calculator