Field guides.
37 worked explanations behind the tools: the formulas, the sources and where each model stops.
Shelter & camp
Most tarp questions are geometry in disguise: how high, how wide, how much cord. These guides work them through with the same equations as the Shelter studio, then mark where geometry stops and weather, ground and judgement take over.
Shelter & camp hub ↗- 016 min read
A-frame tarp geometry: what ridge height really buys you
Work out A-frame tarp floor width, wall angle and usable headroom from ridge height, with a table for a 3 m tarp and the formulas behind it.
- 026 min read
What size tarp do you need for camping?
Choose tarp size for camping: floor width, wall angle, sleeping length and fabric area for 2×3, 3×3 and 3×4 m tarps, with the arithmetic shown.
- 035 min read
How much guyline does a tarp need? End guys and ridgelines worked out
Work out tarp guyline length from ridge height and stake distance, then add a ridgeline allowance for tree spacing, trunk wraps and knots.
- 046 min read
How to pitch a tarp for wind: ridge height, orientation and tension
Pitch a tarp for wind by lowering the ridge, turning an open end away from the wind and keeping guylines tight, with the cost in headroom.
- 057 min read
Choosing a campsite: overhead hazards, ground and where the sun comes up
How to choose a campsite: check rules, overhead hazards, drainage and sleeping ground, then use sunrise bearing to place the open end of a tarp.
Pace, load & food
Time, weight and food are linked. A heavier pack slows you down and burns more energy, and the food that covers the energy is itself weight. Naismith, Tobler and Pandolf each model one part of that loop.
Pace, load & food hub ↗- 016 min read
Naismith’s rule, with the corrections that make it useful
Naismith’s rule in metric: 5 km/h plus 10 minutes per 100 m of ascent, with Langmuir descent corrections and a worked 14 km hiking time example.
- 025 min read
Tobler’s hiking function: how walking speed changes with slope
Tobler’s hiking function gives walking speed on a slope: 6 × e^(−3.5 |S + 0.05|) km/h. See the speed table, the flat value and a map-based example.
- 035 min read
The Pandolf equation: what a backpack adds to walking energy
The Pandolf equation estimates walking energy with a pack. A 75 kg walker with 12 kg at 4 km/h on a 3% grade uses about 327 kcal in one hour.
- 045 min read
Base weight: the ledger behind a pack’s total weight
Base weight is pack gear without food, water or fuel. Learn what counts, how skin-out weight differs, and a worked ledger reaching 5,700 g.
- 055 min read
Backpacking food weight: turning a calorie target into grams
Work out backpacking food weight from calories and energy density. 2,800 kcal per day at 450 kcal per 100 g is 653 g per day with 5% packaging.
Water treatment
Every treatment addresses some germs and not others, and none of them makes chemically contaminated water usable. These guides follow CDC backcountry guidance on boiling, filtering, chemical disinfection, UV and cloudy water.
Water treatment hub ↗- 015 min read
How long to boil water: the 1-minute and 3-minute rule explained
How long to boil water to kill germs: 1 minute at a rolling boil, or 3 minutes above 6,500 ft (1,981 m), with altitude, cooling and the limits.
- 025 min read
Water filters and purifiers: what a pore size removes, and what it misses
Water filter vs purifier explained: which absolute pore sizes and NSF certifications remove parasites, bacteria and viruses, and what to check on a label.
- 035 min read
Chemical water treatment: what each disinfectant kills, and what it misses
Chemical water treatment compared: what bleach, iodine and chlorine dioxide kill, what they miss, EPA bleach figures and the iodine cautions.
- 045 min read
Cloudy water: let it settle or filter it before any treatment step
How to treat cloudy water when camping: settle or strain it through clean cloth, draw off the clear water, then boil or disinfect. Why cloudiness matters.
- 055 min read
UV water treatment: what a portable UV device can and cannot do
UV water purifier explained: what portable UV devices kill, why cloudy water and battery power matter, and what UV leaves in the water.
Weather & altitude
Forecasts describe the air at a weather station. These guides translate the numbers for exposed skin, long climbs and high camps, and set out what official lightning guidance actually says.
Weather & altitude hub ↗- 016 min read
Wind chill explained: the formula, its limits and what it measures
Wind chill formula for hikers in °F and °C, with a chart in °C and km/h, worked examples, the NWS limits and what the index does not include.
- 026 min read
Heat index while hiking: what the number means and where it stops
Heat index for hiking explained: the NWS formula, a °C version of the NWS categories, a worked example at 32 °C and 60%, and the limits of shade-based readings.
- 035 min read
How much colder it gets with height, and which lapse rate to use
Temperature drop with altitude per 1,000 m and per 1,000 ft, from NASA’s standard-atmosphere equation and NWS lapse rates, with a trailhead example.
- 045 min read
Water boils at a lower temperature at altitude: the numbers and the reasons
Boiling point of water at altitude from the standard atmosphere and the Antoine equation, with a table by elevation, a 10,000 ft example and weather effects.
- 056 min read
Lightning safety while hiking: leave exposed ground before storms arrive
Lightning safety for hikers from NWS guidance: what counts as safe shelter, the 30-minute rule after thunder, flash-to-bang distance and storm timing.
Power & batteries
Battery labels mix units, and solar panel ratings describe laboratory sunlight. These guides convert everything to watt-hours, state the efficiency assumptions openly and show where cold and cloud change the budget.
Power & batteries hub ↗- 016 min read
Converting mAh to watt-hours, and why Wh is the figure to compare
Convert mAh to watt-hours with Wh = mAh ÷ 1,000 × volts, and see where 10,000 to 30,000 mAh banks sit against the 100 Wh and 160 Wh airline limits.
- 026 min read
How many phone charges a power bank gives, and how to estimate it
Estimate phone charges from a power bank by dividing usable watt-hours by the phone battery energy, with 60% and 80% scenarios for a 10,000 mAh bank.
- 037 min read
How much power a portable solar panel makes on a trip
Estimate daily solar charge from panel watts, equivalent sun hours and charging losses, with angle and cloud scenarios for a 10 W backpacking panel.
- 046 min read
Why batteries deliver less energy in the cold, and how to plan for it
Why a phone or power bank delivers less energy in cold weather, how to model the loss as a lower efficiency scenario, and what to do on the trip.
Knots & cord
Camp knots and cord for practice and for jobs such as guylines and ridgelines. None of these guides rates a knot for climbing, rescue or lifting; learn those from a qualified instructor.
Knots & cord hub ↗- 016 min read
How to tie a figure-eight stopper knot, and tell it from an overhand
Tie a figure-eight stopper knot in four steps, recognise a correct one by its two lobes, and compare it with an overhand stopper. Practice only.
- 026 min read
Tying a round turn and two half hitches to a fixed camp post
Tie a round turn and two half hitches around a fixed post or tree at camp, check the knot before you rely on it, and untie it after load.
- 036 min read
Why knot strength percentages disagree, and why none is a working load
Why published knot strength percentages disagree, why breaking strength is not a working load, and what the Knot bench retention figure does.
- 046 min read
Choosing guyline cord: stretch, knot creep and construction
Guyline cord materials compared: nylon, polyester and UHMWPE on stretch, knot creep and friction heat, plus construction, diameter and reflective tracers.
Trip planning
Planning ties the other topics together: time from the route, light from the sun, energy from the pack and water from the source, in a plan that still works without signal.
Trip planning hub ↗- 017 min read
Turnaround time: setting the clock before you start a hike
Work out a hiking turnaround time from sunset, the return leg, breaks and a safety margin, with a worked example and the limits of Naismith’s rule.
- 026 min read
Offline trip planning: what to save, test and leave behind before a hike
Offline hiking checklist: save maps, test them in airplane mode, budget battery power, note daylight and leave a trip plan before you lose mobile signal.
- 036 min read
The ten essentials: a list of systems you scale to the trip
The ten essentials for hiking as ten systems, with the problem each one solves, links to Trailwright guides and tools, and how to scale the list.