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.
What Today's Grocery Shelf Labels Actually Mean
Modern cans are labeled in ounces rather than the old numbered system, but the numbers still map cleanly onto the sizes above. A can labeled "15 oz" on today's shelf is essentially the #300/#303 size — it's the most common vegetable can in any US grocery store, used for green beans, corn, peas, and mixed vegetables, and holds about 1⅞ cups. A "28 oz" can is the #2½ size, still the standard for whole and crushed tomatoes and large-format sauces. Anything labeled "32 oz" or larger on a store shelf is typically closer to a #3 Cylinder or a scaled-down #10, common for broths, large pasta sauces, and bulk beans.
Why "Drained" and "Undrained" Give Different Cup Counts
The cup figures in the chart above are the can's total fill capacity — product plus packing liquid — which is what matters when you're substituting a can into an old recipe that just says "one #303 can of X." But a lot of modern recipes specify a drained measurement instead, and that number is smaller. A standard 15 oz (#300/#303) can of beans, for example, holds about 1⅞ cups total, but once drained, the beans themselves measure closer to 1½ cups — roughly 80% of the can's stated volume, with the rest being packing liquid. Vegetables like corn and peas drain closer to their full stated volume since they hold less liquid by proportion; beans and chickpeas lose the most to draining.
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.
How do I convert a can size from a European or metric recipe?
European recipes typically label cans in grams rather than ounces or numbers, and the two most common sizes — 400g and 800g — line up closely with US grocery sizes without an exact match. A 400g can is close to a US 15 oz can (slightly smaller, about 1.7 cups vs 1.875 cups), and an 800g can is close to a US 28 oz can (slightly larger, about 3.4 cups vs 3.5 cups). For most recipes the difference is small enough to substitute directly; for baking or canning where precision matters more, use the gram or milliliter figure directly rather than converting to the nearest US size.