Your cooler claims it holds ice for days. Weigh the meltwater and find out what it really does.

Features

• One number for your cooler

  Put ice in, wait a few hours, weigh the water that collected. ChillTest turns that into a single heat-leak figure in watts per degree — a property of the box itself, not of the day you tested it.

• Physics, not a guess

  Melting ice holds the inside of a cooler at freezing, and it takes a fixed 333.55 kJ to melt a kilogram of it. Every gram of meltwater is a known amount of heat that got in, so the result is measured rather than estimated.

• A kitchen scale is the whole kit

  No thermometer, no sensor to pair, nothing left inside the box. A measuring cup works too if that is what you have on hand.

• Answers for the trip you are packing for

  How long 10 lb of ice lasts at 90°F, how much ice a two-night trip needs, whether the expensive rotomolded chest really doubles the cheap one. Adjust for lid opening, sun and how full the box is.

• It refuses to show a wrong number

  If the ice melted out, if a gel pack was used instead of ice, or if it was barely warmer outside than in, the run is not a valid measurement — so no figure appears. You get an explanation of what to change instead.

• Every cooler you own, ranked

  Keep as many boxes as you like, each with its own measurement history, sorted best-first. The ranking is yours, measured in your conditions, not copied from a spec sheet.