Hydration guide
Water Conversion Chart: Litres, Ounces, Cups and Bottles
Hydration figures become confusing when a target is written in litres, a bottle is labelled in millilitres and an article uses cups or fluid ounces. The conversions below make those units comparable while keeping an important distinction: UK imperial and US fluid ounces are not the same size.
The conversion rules
One litre equals 1,000 millilitres. One US fluid ounce is about 29.57 ml, while one UK imperial fluid ounce is about 28.41 ml. A US customary cup is about 236.6 ml; HydrateWise also shows 250 ml metric-cup equivalents because they are simple to use for daily planning.
To convert litres to millilitres, multiply by 1,000. To convert millilitres to litres, divide by 1,000. For US fluid ounces, divide millilitres by 29.57. For UK fluid ounces, divide by 28.41. Keep one decimal place for planning rather than implying laboratory accuracy.
Quick daily-fluid conversion chart
1.5 L is 1,500 ml, about 50.7 US fl oz, 52.8 UK fl oz, six 250 ml cups or three 500 ml bottles. 2 L is 2,000 ml, about 67.6 US fl oz, 70.4 UK fl oz, eight 250 ml cups or four 500 ml bottles.
2.5 L is 2,500 ml, about 84.5 US fl oz, 88.0 UK fl oz, ten 250 ml cups or five 500 ml bottles. 3 L is 3,000 ml, about 101.4 US fl oz, 105.6 UK fl oz, twelve 250 ml cups or four 750 ml bottles.
Bottle-size conversions
A 330 ml bottle is about 11.2 US fl oz. A 500 ml bottle is about 16.9 US fl oz. A 600 ml bottle is about 20.3 US fl oz. A 750 ml bottle is about 25.4 US fl oz, and a 1 litre bottle is about 33.8 US fl oz.
Bottle labels usually provide the most reliable capacity. A household glass or mug may vary substantially, so measure it once if you want to use it for repeatable tracking. The number printed on a reusable bottle may describe maximum capacity rather than the comfortable filled volume.
Why cup measurements disagree
“Cup” is not one worldwide unit. A US customary cup is approximately 236.6 ml, a metric cup is 250 ml, and recipes may use still other conventions. That is why two hydration articles can produce different cup totals from the same litre value without disagreeing about the underlying volume.
For a daily routine, choose one definition and label it. Millilitres are the clearest bridge between a calculator, product label and bottle planner. Cups remain useful as a familiar visual estimate.
Conversion does not determine need
Changing units cannot make a fluid target more personal. Weight, activity, conditions, food, other drinks and health circumstances still determine whether the starting estimate is appropriate. Use a conversion only after deciding what number you are converting.
Avoid rounding a partial bottle up and then treating the larger total as mandatory. Small differences disappear within the uncertainty of a general estimate. HydrateWise provides educational planning estimates, not medical advice. Kidney, heart and liver conditions, pregnancy, acute illness and some medicines can change safe fluid intake. Personal clinical guidance takes priority.
Sources and further reading
Free practical resources
Keep the useful numbers close
These resources contain general planning information only. They do not store calculator inputs or include personal health details.
Hydration conversion chart
Litres, millilitres, UK fluid ounces, US fluid ounces, metric cups and common bottle sizes.
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