Dry ice in an insulated cooler typically sublimates at about 5 to 10 pounds every 24 hours, so a 10-pound supply generally lasts roughly one to two days. Linde, a major industrial gas supplier, says that amount per day will keep the contents of a container of up to 15 quarts frozen, and that larger containers or longer trips need proportionally more dry ice.
The exact rate depends on the surrounding temperature, air pressure, and the thickness of the cooler’s insulation. Linde’s best-performing shipper, a urethane box with three-inch walls, lost only 5 pounds a day for a 10-quart storage area. Filling empty space with crumpled newspaper or a paper bag helps, because dead air space makes dry ice sublimate faster, and a larger load of dry ice lasts longer than a small one. For frozen food, Linde’s packing table suggests 7 pounds of dry ice for 5 pounds of food over 24 hours, and 12 pounds for two days. Because dry ice stays at −109.3°F (−78.5°C), it keeps everything frozen until it is completely gone, and the food then takes extra time to thaw.
Source: Linde: How Long Does Dry Ice Last?
Image: Dry ice containers, by Pleple2000, CC BY-SA 3.0, via Wikimedia Commons.
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