Field tools.
Twelve calculators for the questions before a trip. Each one shows its model, its units and where it stops.
Shelter & cord
Geometry and practice for the camp itself.
- 01Shelter studioSee what fits under your tarp. Pitch height, usable floor and line lengths.
ReadA-frame tarp geometry: what ridge height really buys youWhat size tarp do you need for camping?How much guyline does a tarp need? End guys and ridgelines worked out
- 03Knot benchFollow the path. Understand the limits. Step diagrams and material tradeoffs.
ReadHow to tie a figure-eight stopper knot, and tell it from an overhandTying a round turn and two half hitches to a fixed camp postWhy knot strength percentages disagree, and why none is a working load
Moving & carrying
Time, energy, weight and food for the route.
- 02Loaded milesCompare the cost of carrying it. Pack mass, walking speed and uphill grade.
ReadThe Pandolf equation: what a backpack adds to walking energyBase weight: the ledger behind a pack’s total weightBackpacking food weight: turning a calorie target into grams
- 07Trail timeKnow how long the route will take. Naismith time, descent corrections and finish time.
ReadNaismith’s rule, with the corrections that make it usefulLightning safety while hiking: leave exposed ground before storms arriveTurnaround time: setting the clock before you start a hike
- 11Pack ledgerKnow what the pack weighs, and why. Base weight, consumables, total and skin-out.
ReadBase weight: the ledger behind a pack’s total weightThe Pandolf equation: what a backpack adds to walking energy
- 12Food carryTurn calories into grams. Daily energy and food density into carried weight.
ReadBackpacking food weight: turning a calorie target into gramsThe ten essentials: a list of systems you scale to the trip
Map & sky
Slope from contours, the sun’s bearing and the light that is left.
- 04Sun & daylightGive daylight a place in your plan. Sun bearing, sunset and civil twilight.
ReadChoosing a campsite: overhead hazards, ground and where the sun comes upMagnetic declination: converting between true and magnetic bearingsSunset is not the end of usable light: planning a walk-out by the clock
- 08Map slopeRead steepness straight off the map. Contours and map distance into grade and pace.
ReadTobler’s hiking function: how walking speed changes with slopeCalculating slope from contour lines on a paper mapPercent grade and degrees describe the same slope in two ways
Water, weather & power
Treatment choices, felt temperature, altitude and the energy budget.
- 05Water decisionsChoose a treatment, with its limits. Germs, cloudy water and contamination.
ReadHow long to boil water: the 1-minute and 3-minute rule explainedWater filters and purifiers: what a pore size removes, and what it missesChemical water treatment: what each disinfectant kills, and what it misses
- 06Power budgetMake every watt-hour count. Device draw, batteries and solar scenarios.
ReadConverting mAh to watt-hours, and why Wh is the figure to compareHow many phone charges a power bank gives, and how to estimate itHow much power a portable solar panel makes on a trip
- 09Feels likeAdd wind and humidity to the forecast. Wind chill and heat index, with risk bands.
ReadWind chill explained: the formula, its limits and what it measuresHeat index while hiking: what the number means and where it stopsHow to pitch a tarp for wind: ridge height, orientation and tension
- 10AltitudeSee what changes higher up. Air pressure, boiling point and summit temperature.
ReadHow much colder it gets with height, and which lapse rate to useWater boils at a lower temperature at altitude: the numbers and the reasonsHow long to boil water: the 1-minute and 3-minute rule explained
How the tools work
Every calculation runs in your browser; nothing you type is sent anywhere. Each tool can save its inputs on this device, and the whole set works offline once the field pack is saved. The equations, units and limits are on the method page, and the field guides work through real examples with each one.