How many ice packs do I need for a cooler? Work it from the two numbers the makers publish

The method, in one line

Every rule of thumb you will read on this question — “two packs per cooler”, “one pack per six cans” — is invented, because packs come in wildly different sizes. What is published, and therefore usable, is two figures:

One. How much ice your cooler holds. Hard-cooler makers publish this. RTIC states 41 lb of ice for the 45 QT Ultra-Tough, 58 lb for the 65 QT Ultra-Tough and 51 lb for the 52 QT Ultra-Light. YETI expresses the same idea as can count at a ratio: 28 cans at a 2:1 ice-to-can ratio for the Tundra 45 and 42 cans at 2:1 for the Tundra 65.

Two. How much ice one pack replaces. Cooler Shock states its mid-size packs each replace 5-6 lb of ice. Most brands do not publish this at all, in which case use the pack's own weight as a rough stand-in — a YETI ICE Sheet (Large) is 2.2 lb, an Igloo MaxCold two-pack is 2.03 lb for the pair, an Engel 5 lb pack is in its name.

Worked for a 45 and a 65

A 45-quart cooler. 41 lb of ice capacity (RTIC's figure) ÷ 5-6 lb per pack = seven to eight Cooler Shock mid-size packs to fully replace the ice. In practice nobody does that, because you also want food in there: four or five packs around the contents plus a few pounds of loose cubed ice to fill the voids is the configuration that actually works.

A 65-quart cooler. 58 lb ÷ 5-6 lb = ten to twelve packs for a full replacement; six to eight plus loose ice in the gaps for a real trip.

A lunch cooler or a small soft cooler. One or two small packs. YETI is explicit about this case: it describes the ICE Sheet as “engineered to completely replace the need for regular ice inside your Hopper Soft Coolers and Daytrip Lunch Bag and Box”. At that size a single hard pack really is the whole cooling load — see best lunch coolers.

If you are sizing the cooler rather than the ice, start at what size cooler do I need — the two decisions are the same decision.

Where packs beat ice, and where they lose

Packs win on four things. They do not flood the cooler with meltwater, so sandwiches survive and a hunting cooler drains less often. They are reusable, which matters if the cooler goes out weekly. They can be frozen harder than water ice — Outdoor Life measured starting temperatures of 5°F for the Igloo MaxCold block, 4°F for Cooler Shock, -5°F for the YETI sheet and 1°F for the small RTIC pack — so they begin with cold in hand that a 32°F bag of ice does not have. And they hold a shape, so they stack against the walls where most of the heat comes in.

Packs lose on two things, and both are decisive for a long trip. They do not fill voids. Loose cubed ice pours into the gaps between cans and packages and makes thermal contact everywhere; a rectangular pack touches three things and leaves air around the rest. And you cannot buy more at a gas station. On a five-day trip the cooler that gets re-iced on day three wins, and that cooler is running on bagged ice.

So the honest answer for most trips is a mix: packs against the walls and the lid, loose ice filling everything else. Block ice vs cubed ice covers the same trade between the two kinds of water ice, and how to keep ice longer in a cooler is the full checklist.

Read the phase-change temperature before you buy

This is the spec that separates a pack that keeps drinks cold from a pack that keeps food safe, and it is published.

Cooler Shock states an 18°F phase change point and claims it “keeps contents colder longer than standard ice, maintaining safe temps for up to 48 hours in a size-matched cooler”. Engel publishes 32°F for its 2.5 lb and 5 lb Cooler Packs and 28°F for the 0.75 lb pack. A sub-freezing phase change means the pack holds the cooler below freezing while it thaws, which will freeze lettuce and beer against it; a 32°F pack behaves like ice and holds the cooler at refrigerator temperatures.

Pick the sub-freezing packs for meat, fish and a cooler that must not go above 40°F. Pick 32°F packs for a cooler full of drinks and produce you do not want frozen solid. Nothing on this page has been measured inside a cooler by anyone — Outdoor Life's numbers are a four-hour test on a counter after a 36-hour freeze, which ranks the packs against each other but is not a cooler result.