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How much water should you drink a day if you weigh 120 lbs?
At 120 lbs (54 kg), aim for about 61 fl oz (1.8 litres) a day if you mostly sit, and more on active or hot days.
Updated October 17, 2026
61 fl oz a day
About 1.8 litres, 7 glasses or 3.5 standard 16.9 oz bottles, if you mostly sit. More if you're active or it's hot.
By activity and weather
| Your day | Normal day | Hot day |
|---|---|---|
| Mostly sitting | 61 fl oz (1.8 L) | 78 fl oz (2.3 L) |
| Lightly active | 73 fl oz (2.1 L) | 89 fl oz (2.6 L) |
| Very active | 84 fl oz (2.5 L) | 101 fl oz (3.0 L) |
These come from 33 ml per kilogram of body weight (120 lb is 54 kg, so 54 × 33 = 1.8 L), plus 350 ml for a lightly active day or 700 ml for a very active one, and 500 ml more in the heat.
That's a little below the US National Academies' general figure for women (about 2.2 L from drinks), which makes sense: those figures are averages for adults of all sizes, and lighter bodies need less.
Spread it across your day
3.5 bottles is easier to picture than 61 fl oz. The simplest plan is one 16.9 oz bottle about every 4 hours between 7 am and 9 pm, starting with a glass when you wake up. Steady drinking also suits your kidneys, which can only clear about a litre an hour.
Training today? The American College of Sports Medicine suggests about 0.4–0.8 litres for each hour of exercise, on top of your daily amount.
Try other numbers
Change the weight, activity or weather to see your exact amount.
Questions people ask
Is 95 fl oz too much at 120 lbs?
Spread across a day, no. Healthy kidneys can handle far more than that. What matters is pace: drinking more than about a litre an hour for several hours is what gets risky.
Do coffee and tea count toward my water?
Yes. A study that gave regular coffee drinkers four cups a day found they stayed just as hydrated as when they drank the same amount of water. Water is still the best default because it has no sugar or caffeine.
Should I drink more if I take creatine?
A sensible buffer is about 500 ml (17 oz) on top of your daily amount, plus a glass with each dose. That puts you at about 78 fl oz (2.3 litres).
Sources
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