Water Requirements Calculator
Estimate how much water to carry on your hike
One carry period at a time. Calculate from your start, or your last reliable refill, to your next reliable refill or the end of the hike. For a dry section that spans several days, add the walking and break times together, and leave out overnight sleep and camp time.
Your Water Plan
How this was worked out
This is a planning estimate, not a drinking target. Your needs can vary substantially with conditions, effort and individual sweat rate. Drink according to your needs and avoid forcing fluids simply to match the estimate.
The THA planning scale (litres per hour)
| Conditions | Easy | Moderate | Strenuous |
|---|---|---|---|
| Below 15°C (cool or colder) | 0.30 | 0.40 | 0.50 |
| Mild, 15 to below 25°C | 0.35 | 0.50 | 0.65 |
| Warm, 25 to below 30°C | 0.45 | 0.65 | 0.80 |
| Hot, 30 to below 35°C | 0.55 | 0.75 | 0.95 |
| Very hot, 35°C or above | 0.65 | 0.90 | 1.10 |
Rates are THA planning assumptions. ACSM and Wilderness Medical Society guidance informs the explanation of individual variation and drinking behaviour; it does not establish these rates. The highest value is the top of the scale, not a maximum need or a safe drinking limit.
This tool provides planning guidance based on the information you enter. Results are estimates, not confirmation that a hike is safe or suitable for your group. Check current conditions and access, consider everyone's capabilities, and adjust your plan when circumstances change.
Before you leave, share your trip plan and expected return time with a trusted person, and agree what they should do if you do not return.
The calculated amount is a planning estimate, not a prescribed drinking target. Check refill reliability and container capacity.
Water Requirements Calculator
Why water planning matters more than most hikers realise
Water is the most safety-critical variable in Australian hiking. Unlike a navigation error that announces itself when you realise you are off track, dehydration degrades performance gradually and quietly. Concentration drops before thirst becomes obvious. Judgement narrows before a hiker feels unwell. By the time dehydration is noticeable, it has often been affecting decision quality for some time. In hot Australian conditions, the margin between adequate hydration and a serious problem can close quickly, particularly when terrain is rough, the route is exposed, or the pace is higher than planned.
What the calculator accounts for
Water needs on a hike are not fixed. They vary with temperature, effort, load, and sun exposure. The calculator asks for three things: your estimated hike time (including planned breaks), the expected temperature, and your effort level. Effort is your overall judgement of how hard the walk will be, taking climbing, terrain, pace and your loaded pack together: easy, moderate or strenuous. Temperature and effort together give an hourly rate from the Trail Hiking Australia planning scale below. If you know how much you usually drink per hour, you can enter your own rate instead, and it is not capped.
| Litres per hour | Easy | Moderate | Strenuous |
|---|---|---|---|
| Below 15°C (cool or colder) | 0.30 | 0.40 | 0.50 |
| Mild, 15 to below 25°C | 0.35 | 0.50 | 0.65 |
| Warm, 25 to below 30°C | 0.45 | 0.65 | 0.80 |
| Hot, 30 to below 35°C | 0.55 | 0.75 | 0.95 |
| Very hot, 35°C or above | 0.65 | 0.90 | 1.10 |
The estimate is then worked out like this: water to carry = rate × hike time + rate × extra time for delays + camp water
The extra time for delays is one hour unless you change it, and camp water is whatever you enter for camp use and cooking. For example, a 5 hour hike in mild conditions at moderate effort is 0.50 × 5 + 0.50 × 1 = 3.00 litres. You can also enter the capacity of your containers, and the calculator will tell you if the estimate is more than you can carry. The scale is a set of Trail Hiking Australia planning assumptions informed by hydration guidance. It does not establish how much any one person needs, and the highest figure in the table is not a maximum. Direct sun, limited shade and humidity can increase heat strain and make the estimate less representative.
Planning for multi-day and overnight hikes
The calculator works on one carry period at a time: from your start, or your last reliable refill, to your next reliable refill or the end of the hike. For multi-day hikes, run it separately for each carry period. If a dry section spans several days, add the walking and break times together for your hike time, and leave out overnight sleep and camp time. Then enter the water you will use at camp for drinking and cooking in the camp water box, so it is counted once. The refill field at the bottom of the form helps you think through resupply: selecting no reliable refill, uncertain refill, or reliable refill produces a corresponding planning note to guide your decision on starting carry. Water planning for multi-day routes directly affects the Load Carrying and Mobility system, since heavier water loads change pack weight, fatigue rate, and balance.
Connecting to the Hydration and Fuel system
Within the Hiking Safety Systems Framework, the Hydration and Fuel system sustains physical output, cognitive function, and temperature regulation across the duration of a hike. When this system starts to fail, the effects are felt across multiple other systems: navigation accuracy drops, decision quality deteriorates, heat regulation becomes less effective, and fatigue accelerates. The Water Requirements Calculator is a direct planning tool for this system, helping hikers establish a realistic starting carry rather than relying on a general rule that may not reflect actual conditions.
Using the result
The result is a planning estimate, not a prescribed drinking target. Your needs can vary substantially with conditions, effort and your own sweat rate, so drink to your needs and avoid forcing fluids just to match the number. The extra time for delays is a planning assumption, not a measured safety margin, and it exists because conditions on the day may differ from plan: the pace may be slower, the temperature higher, the terrain more demanding, or a water source may be dry. Increase it if you expect delays, and use your own rate if you know you drink more than the scale suggests. Hikers who run hot, those unacclimatised to heat, and those in larger groups where social dynamics may discourage stopping to drink should consider carrying more. In hot and very hot conditions, carrying more water does not remove heat risk: consider a cooler start, a shorter route or postponing. Check that any refill is reliable, and that you can treat or drink the water, before relying on it. If you are not sure, carry the full estimate. For the hike time to enter, use the estimate from our Hiking Time Calculator. Before you leave, share your trip plan and expected return time with a trusted person, and agree what they should do if you do not return.
Plan Your Hike in Six Steps
The tools below help you assess whether a hike is achievable, understand terrain difficulty, estimate walking time, plan hydration, identify key risks, and determine what equipment to carry before heading out.
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