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About this tool
Before, during and after fluid plan for heated yoga, from a measured weigh-in sweat rate or your room temperature and class style.
The Hot Yoga Hydration Calculator turns a hot yoga class into a fluid plan: how much to drink in the hours before, how much to sip during, and how much to replace afterwards. It uses the sweat-rate equation from the ACSM Position Stand on Exercise and Fluid Replacement — sweat loss equals pre-class weight minus post-class weight plus anything drunk — and applies the same guideline's targets of 5-7 mL per kg beforehand, keeping body-mass loss under 2%, and replacing 125-150% of any remaining deficit. If you have not weighed yourself, it will model a sweat rate from room temperature, humidity, class style and body size instead.
Open Hot Yoga Hydration Calculator on AltFTool — it loads instantly in your browser.
Choose "Estimate it from the room" or "I weighed before and after", then set the Class length (minutes); in estimate mode add Body weight (kg), Room temperature (C), Relative humidity (%) and a Class style of Gentle / hot yin / restorative, Hot vinyasa / Bikram sequence, or Power / sculpt with weights.
In weigh-in mode enter Weight before class (kg), Weight after class (kg) and Fluid drunk during class (ml) instead, and tick "Add the 2-hour top-up (urine dark or none passed since waking)" if you started the day short.
"Carry into class" gives the millilitres to take in and the sip size to drink every 15 minutes, while the list below splits before class, the 2-hour top-up, during, after and the total, alongside sweat rate, sweat lost, deficit percentage against the 2% threshold and sodium lost; Copy plan copies it as text.
Weigh-in mode gives your real sweat rate instead of a population average.
Separates prehydration, in-class sips and post-class replacement so nothing is drunk all at once.
Estimates sweat sodium at roughly 1,150 mg per litre so you know when water alone is not enough.
About 5-7 mL per kilogram of body weight roughly four hours before class — that is 350-490 mL for a 70 kg person. If you produce no urine in that window or it is dark, the ACSM suggests a further 3-5 mL/kg about two hours before.
Commonly 1.0-1.5 litres in a 90-minute heated class, which is a sweat rate near 0.7-1.0 L per hour. It varies widely with room temperature, humidity, body size and fitness, so weighing yourself before and after is the only reliable way to know your own figure.
Weigh yourself undressed before class and again afterwards towelled dry, then add whatever you drank: sweat loss in litres equals the weight drop in kilograms plus the fluid drunk in litres. Divide by class length in hours for a rate in litres per hour.
Water is usually enough below about a litre of sweat loss. Past that you are also losing roughly 1,150 mg of sodium per litre, and replacing large volumes with plain water can dilute blood sodium — add salt through food or an electrolyte drink. This is general information; anyone with kidney, heart or blood-pressure conditions should ask their doctor.
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