Why Can Sizes Use Numbers Instead of Ounces
The numbered can-size system (#1, #303, #10, and so on) dates back to the early 1900s US canning industry, when can dimensions — not fluid volume — determined the number. It became the standard reference on recipe cards and cookbooks through the mid-20th century, which is why a lot of older recipes still say "one #2½ can of tomatoes" instead of a weight or cup measurement. Modern grocery cans are labeled in ounces, so converting an old recipe means matching the can number to its actual volume.
What to Buy If You Don't Have the Exact Can
Grocery stores mostly stock #303 (16 oz) and #2½ (28-29 oz) cans today — the other sizes are either historical, restaurant/institutional-only (#10), or region-specific. If a recipe calls for a size you can't find, use the chart above to match cups rather than guessing: two #303 cans (4 cups total) is close to one #2 can plus a bit extra, and roughly six #303 cans approximate one restaurant-size #10 can.
Frequently Asked Questions
How many cups are in a #10 can?
A #10 can holds about 12-13 cups (roughly 6.5-7 lbs / 109-117 oz of product). It's the large institutional size used by restaurants and food banks, not typically sold at grocery stores — if a recipe calls for one and you only have grocery-size cans, you'll need about six #303 (16 oz) cans to match it.
What's the difference between a #303 can and a #2 can?
A #303 can holds about 2 cups (16-17 oz) and is the standard size for most canned vegetables and beans on grocery shelves. A #2 can is larger, holding about 2.5 cups (20 oz) — it's less common today but still shows up for pineapple and some juices.
Why do old recipes reference can sizes like #2½ instead of ounces?
The numbered can-size system dates to the early 1900s US canning industry and was standard on recipe cards and cookbooks through the mid-20th century. Modern cans are usually labeled in ounces instead, so a recipe written decades ago often needs converting — a #2½ can (28-29 oz, about 3.5 cups) was the standard size for canned tomatoes and fruit.