Hydration is one of the most overlooked aspects of nutrition, yet it plays a critical role in metabolism, digestion, temperature regulation, and overall health.
Unlike calories or macronutrients, water needs are not exact — but several well-established formulas help estimate daily fluid requirements.
1. Basic Weight-Based Formula (30–35 mL/kg)
This is one of the simplest and most widely used methods in nutrition practice.
Fluid Needs = weight (kg) × 35 mL → maximum
Example — 70 kg person
Maximum: 70 × 35 = 2,450 mL/day
Range: 2,100 – 2,450 mL/day
2. Holiday-Segar Method (Clinical Standard)
Commonly used in clinical settings for more individualized hydration needs. It uses a tiered calculation based on body weight.
Next 10 kg → 50 mL per kg
Remaining → 20 mL per kg
Example — 70 kg person
Next 10 kg: 10 × 50 = 500 mL
Remaining 50 kg: 50 × 20 = 1,000 mL
Total: 2,500 mL/day
3. 1 mL per Calorie Method
A practical method often taught in nutrition programs. If you know your calorie intake, this is an easy estimate.
Which Method Should You Use?
| Method | Best For |
|---|---|
| 30–35 mL/kg | General use, quick estimate |
| Holiday-Segar | Clinical settings, more individualized |
| 1 mL/kcal | When daily calorie intake is known |
In practice, all three methods produce similar ranges. Always adjust based on activity level, climate, health conditions, and real-world cues like thirst and urine color.
Final Thoughts
Hydration formulas are not about precision — they're about guidance. Your actual needs can vary daily, so these formulas should be used as a baseline rather than an absolute rule.
Combine these estimates with real-life cues like thirst, urine color, and energy levels. Pair this with the TDEE Calculator for a complete picture of your daily nutrition needs.