Formulas and sources
Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.
Baseline daily water
With no exercise entered
- T
- daily water intake, in US fluid ounces
- W
- body weight, in pounds
Kilograms are converted to pounds first (× 2.20462). Ounces convert to milliliters at 29.5735 per ounce, and a custom goal in liters at 33.814 ounces per liter.
Source: A widely used rule of thumb; no primary source found. Searches of the web and of Europe PMC (a biomedical literature database) found only calculators, blogs and other secondary pages. For comparison, the National Academies' 2005 Adequate Intakes of total water, from drinks and food, are 3.7 L a day for men and 2.7 L for women aged 19 and over [1]. The conversion factors are NIST's, rounded [3].
Daily water with exercise
Light, Moderate and Intense modes, when exercise minutes are entered
- T
- daily water intake, in US fluid ounces
- W
- body weight, in pounds
- E
- minutes of exercise in the day
- I
- intensity multiplier: 1.0 Light, 1.2 Moderate, 1.5 Intense
Source: The 12 ounces per 30 minutes is widely used; no primary source found (same searches). No source was found for the three intensity multipliers. The American College of Sports Medicine's 2007 position stand advises fluid plans fitted to each person's sweat losses [2].
Sources
- Institute of Medicine, National Academies Press. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. 2005.
- Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 2007; 39(2): 377-390.
- National Institute of Standards and Technology. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science, mass and volume. Special Publication 811.
What this calculator does not cover
- It does not use age or sex, and has no separate figures for children. The National Academies' intakes are set by age and sex [1].
- The figure does not say whether it counts drinks only or total water. The Adequate Intakes are for total water, about 20% of it usually from food. They reflect typical intakes, and people can be well hydrated above or below them [1].
- It does not adjust for hot weather, pregnancy or breastfeeding, which can raise fluid needs [1], or for illness such as fever, vomiting or diarrhea.
- It sets no upper limit on the result. At 500 kg, the highest weight it accepts, the baseline alone is about 21.7 L a day.
Sources checked on .