What is the common size of a standard large envelope?

The standard large envelope size is typically recognized as 9.5 inches by 4.125 inches. This size is commonly used for sending items like business letters or documents that require a larger format than standard envelopes. While there are several envelope sizes, this particular dimension aligns with the specifications of large envelopes recognized by postal services.

The other options represent sizes for different types of envelopes: 8.5 inches by 11 inches corresponds to standard letter-sized paper; 6 inches by 9 inches is often used for invitation or greeting cards; and 10 inches by 12 inches, while larger, does not fit the standard classification for what is commonly referred to as a "large envelope." Hence, the first option is the appropriate answer based on standard dimensions for large envelopes.