How Long Does Dry Ice Last? What Actually Determines the Answer

Dry ice lasts about 18 to 24 hours in a well-packed cooler, roughly a day in a home freezer, and three to five hours sitting out at room temperature. Those numbers move because the loss is a share of what you have rather than a fixed number of pounds. The FAA's Civil Aerospace Medical Institute measured 2.0% ± 0.3% of mass lost per hour on five-pound pellet loads in insulated shipping containers (report DOT/FAA/AM-06/19), and FAA Advisory Circular 91-76A recommends that rate for any package under 100 pounds. Two percent an hour works out to roughly half of the remaining mass going every 24 hours. Five pounds is functionally spent in a day. Fifty pounds still has around six pounds left on day three, which is why the USDA says 50 pounds will hold a full 18-cubic-foot freezer for two days.

Why "five to ten pounds a day" only works for one size of load

Every supplier quotes the same rule of thumb, WestAir and Dry Ice Corp among them: dry ice sublimates at five to ten pounds every 24 hours in a properly insulated cooler. It is correct for one range of load and misleading everywhere else.

Run the FAA's 2% per hour against three loads.

| Starting load | Lost in 24 hours at 2%/hr | What the flat rule predicts | |---|---|---| | 5 lb | about 2.4 lb | 5–10 lb: predicts total loss | | 15 lb | about 7 lb | 5–10 lb: agrees | | 50 lb | about 24 lb | 5–10 lb: understates by half |

The flat rule is the percentage rule evaluated at roughly a fifteen-pound load. Buy five pounds and more survives than it says. Buy fifty and you lose far more in absolute terms while doing better per pound, which is what decides whether you reach the end of the job. Air cargo practice draws the same line from the same FAA work: 2% per hour under 45 kg (99 lb), 1% above it. A bigger mass exposes less surface for its weight.

It also cross-checks the USDA figure: fifty pounds shedding half its remaining mass daily leaves about 25 pounds after a day and 13 after two, which is the margin behind the FSIS two-day number.

Six things that decide where you land

Mass does most of the work, and it is what people get wrong when they scale a plan up. Doubling the load more than doubles the hours.

Form comes next. A ten-pound block and ten pounds of rice-sized pellets carry very different surface areas, and surface area is the whole mechanism. Until 2023 I specced pellets for every frozen sampling run, because they pack around product and pull the temperature down fast, and speed was what I was measuring. I stopped after a nine-hour dessert stand ran out of cold with three hours of trading left. Pellets under four hours, block above it.

Insulation thickness is measurable, so check it before you buy. Pelican publishes two inches of polyurethane foam in its Elite coolers, and two to three inches is the range for rotomolded hard coolers. A thin-wall foam picnic chest is a fraction of that and will roughly halve your hours.

Empty space is volume you are paying to keep cold. Pack the gaps with newspaper, towels, or the carpet padding the FAA study used.

Ambient temperature sets the heat load pushing through that foam; a cooler riding in a 90°F vehicle is a different problem from one indoors.

Lid openings are what people underestimate. Carbon dioxide is about 1.5 times denser than air, so it settles into a cold blanket over your contents, and every opening pours it out.

Dry ice against water ice: different substance, different rules

The Compressed Gas Association puts dry ice at −109.3°F (−78.5°C). Water ice sits at 32°F. That 141-degree gap is why the two are not interchangeable, and why their safety rules diverge.

| | Dry ice | Water ice | Frozen gel packs | |---|---|---|---| | Temperature | −109.3°F | 32°F | 0°F to 32°F | | Becomes | CO₂ gas, no liquid | Meltwater | Liquid in a sealed pouch | | Latent heat per lb | ~246 BTU | ~144 BTU | Below water ice | | Holds food frozen | Yes | No | Briefly | | Container | Must vent gas | Any | Any | | Food contact | Freezer burn | Safe | Safe | | Air travel limit | 5.5 lb per person | None | None |

The strongest argument against most of what I recommend is straightforward, and I grant it. Water ice cannot hold anything frozen. It stops at 32°F and it produces water, which puts the FDA's 0°F frozen-storage standard out of reach. If your load must arrive frozen, dry ice is the only widely available option and no thickness of insulation changes that. My answer is narrower than a rejection: most people buying dry ice want food kept cold, not frozen, and for cold they have bought a ventilation problem they did not need.

The BTU row gets quoted carelessly. Dry ice holds a 1.7-to-1 advantage on the phase change alone, but meltwater keeps absorbing heat as it warms while CO₂ gas escapes and takes its capacity with it. Dry ice wins decisively on a deep-frozen target; the margin narrows under 40°F.

A cooler against a household freezer

A home freezer runs at 0°F, still 109 degrees warmer than the dry ice inside it. It barely slows sublimation, so you get roughly the same day a decent cooler gives you, plus two problems the cooler does not have. The extreme cold can trip the appliance thermostat, and Cornell's Environment, Health and Safety office states plainly that dry ice should not go in a refrigerator, freezer, or other enclosed appliance. The same guidance rules out walk-in cold rooms. Use a vented cooler.

Buying and packing it so it lasts

1. Buy it the day you use it. I once moved an order two days earlier to catch a cheaper delivery slot. It sat in a depot cooler over a weekend, about half was gone by the time anyone needed it, and we bought the shortfall at retail on short notice. The saving vanished several times over.
2. Pre-chill the cooler with water ice or a gel pack, then tip it out before loading. Otherwise the foam is the first thing your dry ice cools.
3. Put the dry ice on top, wrapped in paper. Cold sinks, paper slows sublimation, and the wrapping prevents freezer burn.
4. Fill every gap with newspaper, towels, or padding.
5. Leave the lid loose or vented. Never latch a dry-ice cooler airtight.
6. Ventilate the vehicle. The Compressed Gas Association's guidance for a passenger compartment or trunk is to keep the quantity small and keep windows open or fresh air moving for the whole trip.

The mistakes that stop being about money and start being about safety

Pressure does damage fastest. One pound of dry ice becomes roughly 8.8 cubic feet (250 liters) of carbon dioxide gas according to Cornell's dry ice tip sheet. Seal that in a screw-top jar, a latched cooler, or a 12V freezer and you have a burst container. Cornell's instruction is unqualified: never place dry ice in a sealed container.

Carbon dioxide displaces oxygen and is heavier than air, so it accumulates from the floor up in cars, chest freezers, stairwells, and cellars. OSHA's permissible exposure limit is 5,000 ppm as an 8-hour average under 29 CFR 1910.1000 Table Z-1. NIOSH adds a 30,000 ppm short-term limit over 15 minutes and sets the immediately dangerous to life or health level at 40,000 ppm, or 4%. The CGA warns that 3% can already be dangerous and higher concentrations lethal. Five pounds fully sublimated releases about 44 cubic feet of gas, which is why the CGA tells you to drive with the windows down.

Skin contact is third. At −109.3°F dry ice freezes tissue on contact, so it gets handled with insulated gloves and tongs.

The food mistake is the quiet one. Direct contact freezer-burns anything soft and drives chilled product far below its intended temperature, wrecking texture in dairy, produce, and prepared sandwiches. Paper between ice and product separates arriving cold from arriving damaged.

It is already smaller than you expected, or it is in the wrong box

If half is gone early, every remaining option is about heat load rather than the ice. Consolidate the pieces into one mass, wrap them in paper, fill every void, stop opening the lid, and get the cooler out of any hot vehicle. If the contents are frozen food and no more dry ice is available, the FSIS test is whether the food still holds ice crystals or reads 40°F or below; if it does, it is safe to refreeze.

A sealed container gets opened in open air, never in a car or a closed room, with the closure loosened at arm's length. Dry ice in a running freezer comes out; dry ice in a passenger cabin means windows down first.

Sizing it for the actual job

One estimate does not survive four different jobs.

| Job | Working figure | What binds | |---|---|---| | Cooler, 24 hours | ½ to 1 lb per quart of capacity | Insulation and lid discipline | | Frozen shipment | 1.5–2 lb per cubic foot per day, plus 20% margin | Carrier weight caps | | Fog effect | 5 lb into 4–5 gallons of hot water | Water temperature | | Power outage | 2.5–3 lb per cubic foot of freezer space | Supply once the outage starts |

For fog, Penguin Brand Dry Ice and Dry Ice Corp both put peak output in the first five to ten minutes, after which the water cools and the effect thins to nothing below about 50°F. Hot water is the limiting resource, so refresh it every 15 minutes rather than buying more ice.

Shipping is where the numbers turn legal, and I should be clear about my limits. I have never shipped dry ice by air and will not write as though I have. Every air figure below comes from published FAA and USPS text. What I can vouch for is chilled and frozen road distribution, where the binding constraints are delivery windows and vehicle ventilation.

The FAA allows 5.5 pounds (2.5 kg) per passenger in carry-on or checked baggage under 49 CFR 175.10, provided the package vents carbon dioxide, is marked "Dry Ice" or "Carbon Dioxide, Solid" with the net weight, and the airline approves it. USPS Publication 52, Packaging Instruction 9A caps air-eligible mailpieces at five pounds and requires a Class 9 hazard label plus "Dry Ice, UN1845", the net weight, and the contents. Surface mail may exceed five pounds if marked "Surface Only". Ground is far less restricted; FedEx publishes a 200 kg per-package ceiling.

When the answer is to stop buying dry ice

Moving cold loads repeatedly rather than once makes dry ice an expensive habit with a recurring safety cost. For anything that only needs to stay under 40°F, a rotomolded cooler with two to three inches of polyurethane and a 2:1 ice-to-contents ratio holds food-safe temperatures for days without releasing a cubic foot of carbon dioxide. For frozen loads on a repeating route, a 12V compressor fridge-freezer removes the consumable entirely.

Keep dry ice for what only dry ice does: holding 0°F where there is no power, and carrying frozen goods through one long unpowered leg. Everything else is a comparison against a better cooler, and on a repeating route the cooler wins on cost and never needs reordering.

Questions people actually ask

Does dry ice last three days?

Only in quantity. At roughly half the remaining mass lost every 24 hours, five or ten pounds is finished well before day three. Fifty pounds in a full freezer still holds around six pounds on day three, which matches the USDA's two-day guarantee with margin. Plan mass, not days.

How long will five pounds of dry ice last in a cooler?

About 18 to 24 hours of useful cold in a typical hard cooler that gets opened a few times. Five pounds loses roughly 2.4 pounds in the first 24 hours at the FAA's 2% per hour rate, and below a pound or two it can no longer hold temperature. A heavily insulated cooler left shut stretches it toward two days.

How can dry ice be kept from melting?

Dry ice does not melt. It sublimates straight to carbon dioxide gas, and you slow that by reducing surface area and heat. Buy block rather than pellets, wrap it in paper, fill all empty space, keep the cooler out of heat, and open the lid as rarely as the job allows.

How long does dry ice last in a freezer?

Roughly a day, which is about what a decent cooler gives you. A home freezer runs at 0°F, still 109 degrees warmer than dry ice, so it barely slows sublimation. Cornell's environmental health office advises against it outright, because the trapped gas and extreme cold can damage the appliance.

How long does dry ice last when shipping?

Plan on losing about 2% of the package mass per hour, the rate the FAA measured and recommends for packages under 100 pounds. A five-pound load covers roughly 24 hours of transit; 48 hours needs closer to ten pounds. Carrier caps bind first, though: USPS allows five pounds by air.

Why must a dry-ice container be vented?

Because one pound produces about 8.8 cubic feet of carbon dioxide gas as it sublimates. Sealed inside a rigid container, that gas builds pressure until something ruptures. Federal shipping rules under 49 CFR 173.217 require packaging that permits the release of gas, and every safety authority repeats it.