ThirstyBotMost healthy adults need to drink about 54–95 fl oz (1.6–2.8 liters) a day, which is roughly 7 to 12 cups of 8 oz. Where you fall in that range depends on your weight, age, sex and how active you are. This is what you need to drink. Food supplies about another 20% on top. Plain water is the best choice, but tea, coffee and milk count too.
How much water should I drink a day based on weight?
This chart is for people with low activity who are not pregnant or breastfeeding:
| Weight | Women 19–54 | Men 19–54 | Women 55+ | Men 55+ | |
|---|---|---|---|---|---|
| 45 kg | 99 lb | 1,600 ml (54 oz) | 2,000 ml (68 oz) | 1,600 ml (54 oz) | 2,000 ml (68 oz) |
| 50 kg | 110 lb | 1,600 ml (54 oz) | 2,000 ml (68 oz) | 1,600 ml (54 oz) | 2,000 ml (68 oz) |
| 55 kg | 121 lb | 1,600 ml (54 oz) | 2,000 ml (68 oz) | 1,600 ml (54 oz) | 2,000 ml (68 oz) |
| 60 kg | 132 lb | 1,700 ml (57 oz) | 2,000 ml (68 oz) | 1,600 ml (54 oz) | 2,000 ml (68 oz) |
| 65 kg | 143 lb | 1,800 ml (61 oz) | 2,000 ml (68 oz) | 1,600 ml (54 oz) | 2,000 ml (68 oz) |
| 70 kg | 154 lb | 1,950 ml (66 oz) | 2,000 ml (68 oz) | 1,700 ml (57 oz) | 2,000 ml (68 oz) |
| 75 kg | 165 lb | 2,100 ml (71 oz) | 2,100 ml (71 oz) | 1,800 ml (61 oz) | 2,000 ml (68 oz) |
| 80 kg | 176 lb | 2,250 ml (76 oz) | 2,250 ml (76 oz) | 1,900 ml (64 oz) | 2,000 ml (68 oz) |
| 85 kg | 187 lb | 2,400 ml (81 oz) | 2,400 ml (81 oz) | 2,050 ml (69 oz) | 2,050 ml (69 oz) |
| 90 kg | 198 lb | 2,500 ml (85 oz) | 2,500 ml (85 oz) | 2,150 ml (73 oz) | 2,150 ml (73 oz) |
| 95 kg | 209 lb | 2,650 ml (90 oz) | 2,650 ml (90 oz) | 2,300 ml (78 oz) | 2,300 ml (78 oz) |
| 100 kg | 220 lb | 2,800 ml (95 oz) | 2,800 ml (95 oz) | 2,400 ml (81 oz) | 2,400 ml (81 oz) |
Ounces are US fluid ounces, rounded to the nearest whole number. The chart uses the same formula as our water intake calculator and the ThirstyBot app. Teenagers aged 14 to 18 get a slightly higher result, and children under 14 are calculated differently, so use the calculator for them.
How to work out your daily water intake
- Multiply your weight in kg by a rate for your age. The rates come from the Vietnam Ministry of Health’s water requirements (2016): 40 ml/kg for ages 14–18 and for very active adults aged 19–30, 35 ml/kg for ages 19–54, and 30 ml/kg from age 55. If you know your weight in pounds, divide it by 2.2 first.
- Don’t go below the reference for your sex: 2.0 liters for women and 2.5 liters for men. These are the total water intakes (drinks plus food) set by the European Food Safety Authority (EFSA).
- Multiply by 0.8 to get the amount to drink, because about 20% of your daily water comes from food (U.S. National Academies). Round to the nearest 50 ml. To convert to ounces, divide by 29.6.
Example: a 30-year-old woman who weighs 132 lb (60 kg). 60 × 35 = 2,100 ml, which is above her 2,000 ml floor. 2,100 × 0.8 = 1,680 ml, rounded to 1,700 ml (about 57 oz). A man of the same weight and age gets 2,100 ml too, but that is below his 2,500 ml floor, so his goal is 2,500 × 0.8 = 2,000 ml (about 68 oz).
Because of that floor, men under about 70 kg (154 lb) and women under about 57 kg (126 lb) aged 19–54 all get the same number. That is why the top of the chart repeats. Height is not part of the formula.
Is 8 glasses of water a day right?
It is a reasonable rough guide. The NHS in the UK advises aiming for 6 to 8 cups or glasses of fluid a day, and says water, lower-fat milk and lower-sugar drinks, including tea and coffee, all count. The chart above lands in a similar place for most adults, but a light woman may need only about 54 oz, while someone who weighs 220 lb needs closer to 95 oz.
You may also see 2.7 liters (91 oz) for women and 3.7 liters (125 oz) for men from the U.S. National Academies. Those figures are total water from all drinks and food, based on what healthy, well-hydrated Americans typically take in. They are not minimums. About 80% comes from drinks, which works out to roughly 73 oz for women and 100 oz for men.
When do you need more water?
- Exercise: the calculator adds 250 ml (8 oz) for moderate activity and 500 ml (17 oz) for high activity. On workout days, see drinking water before, during and after a workout.
- Hot weather or working in the heat: the NHS says you may need more fluid in hot environments. For outdoor work in the heat, NIOSH advises about 1 cup (8 oz) every 15–20 minutes.
- Pregnancy and breastfeeding: the calculator adds 250 ml (8 oz) when pregnant and 700 ml (24 oz) when breastfeeding.
- Illness: the NHS advises drinking extra fluids when you are unwell. After diarrhoea or vomiting, see signs of dehydration.
Do coffee and tea count toward your water intake?
Yes. According to the U.S. National Academies, caffeinated drinks count toward your total daily water, and the NHS lists tea and coffee among the drinks that count. Keep an eye on the caffeine, though. See how much caffeine per day is safe.
How do you know you’re drinking enough?
The National Academies say most healthy people meet their needs by drinking when they are thirsty. Your urine is a good second check: the NHS says it should be a light yellow. On the 8-colour urine chart, levels 1–3 (almost clear to straw yellow) mean you are hydrated. If remembering is the hard part, spread your goal through the day with a water drinking schedule.
Who shouldn’t use this chart
If you have heart failure, advanced kidney disease or dialysis, low blood sodium (hyponatremia), or a doctor has told you to limit fluids, drink the amount your doctor sets. Healthy people should also avoid drinking a lot in a short time: healthy kidneys can only clear about 0.8–1 liter (27–34 oz) an hour.
Get your exact number
Enter your weight (in kg), age, sex and activity in the water intake calculator to get your own number. The ThirstyBot app uses the same number as your daily goal and reminds you to drink through the day.
ThirstyBot does not replace medical advice. If you have a medical condition, ask your doctor how much water is right for you.
Sources
- NHS – Water, drinks and your health
- Vietnam Ministry of Health / National Institute of Nutrition – Recommended dietary allowances for Vietnamese people (2016), Table 44
- EFSA – Scientific Opinion on Dietary Reference Values for water (2010)
- National Academies – Report sets dietary intake levels for water, salt, and potassium (2004)
- NIOSH / CDC – Heat Stress: Hydration
- HPRC – How to accurately assess hydration status using urine color charts
- Dmitrieva et al. – eBioMedicine 92:104638 (2023)
