How much water to carry hiking, worked out on your iPhone
Last updated 2 June 2026
How much water to carry depends on your body weight, how hard you are working, and the air temperature, so a single fixed number rarely fits. Ferdinands Outdoor Companion (FOC) includes an offline Water Requirements Calculator that takes those three inputs and estimates your daily water need in litres, then converts the figure into a number of 0.5L bottles to pack. It runs entirely on the device, free, with no signal needed. Treat the result as a planning estimate, not a medical figure, and carry a margin.
What the calculator asks for
The FOC Water Requirements Calculator works from three inputs you set with sliders and a menu:
- Body weight, from 40 to 120 kg.
- Activity level, chosen from four options: resting, light, moderate, and intense.
- Air temperature, from 0 to 40 degrees C.
From those it estimates your daily water need in litres, shown to one decimal place, and updates live as you move a slider. Heavier weight, harder activity, and warmer air each push the figure up.
From litres to bottles to pack
A litre figure is useful for planning, but what you actually load is bottles. So the calculator also converts your estimate into a number of 0.5L bottles, rounding up so you are not left short. That turns an abstract number into a concrete packing decision. It sits alongside FOC's other offline tools, including daylight, temperature, and windchill calculators, a packing-list generator, and a step-by-step knot guide.
FOC is free, with no ads, no in-app purchases, and no tracking, and the calculator works fully offline. The estimate is general guidance, not a substitute for judgement: drink to thirst, watch the weather, and plan for resupply points and a reserve.
How it compares
| What matters | FOC | By hand |
|---|---|---|
| Works with no signal | Yes | Yes |
| Adjusts for weight, activity, and temperature | Yes | If you remember the factors |
| Converts litres into 0.5L bottles | Yes | Manual |
| Updates live as you change inputs | Yes | Recalculate each time |
| Ads or tracking | None | None |
| Price | Free | Free |
Frequently asked questions
How much water should I carry on a hike?
It depends on your body weight, how hard you are working, and the temperature, so there is no single right number. FOC's Water Requirements Calculator estimates a daily figure in litres from those three inputs and converts it into 0.5L bottles to pack. Treat it as a planning estimate and carry a margin.
What does the FOC water calculator base its estimate on?
Three inputs: your body weight, an activity level chosen from resting, light, moderate, or intense, and the air temperature. Heavier weight, harder activity, and warmer air each raise the estimated daily water need.
Does the calculator tell me how many bottles to bring?
Yes. After estimating your daily need in litres, it converts the figure into a number of 0.5L bottles, rounding up so you do not pack short.
Does the water calculator work offline?
Yes. The calculator and the rest of FOC run entirely on the device, so it works with no signal and no data connection.
Is the FOC water calculator a medical recommendation?
No. It is a planning estimate to help you pack, not medical advice. Drink to thirst, watch conditions, plan for resupply, and seek proper guidance for any health concern.
Is FOC free?
Yes. FOC is free with no ads, no in-app purchases, and no tracking, and its tools and reference work fully offline.
Related
Sources
This is general reference, not medical, safety, or professional advice. Skills like first aid and foraging carry real risk. In a real emergency, call your local emergency number (112 in the EU, 911 in the US).