I asked this exact question to the guy at the hardware store when I first started, and he laughed and said, "Depends on what you're doing-but there's a sweet spot most people use." From what I've seen and used, the standard size is 10 inches for the blade length. Let me explain why that's the go-to.
First, it matches up with standard brick sizes. A regular brick is about 8 inches long, so a 10-inch trowel gives you enough blade to spread mortar along the brick's length plus a little extra to work with. If you use an 8-inch trowel, you're right at the brick's length-you can't overlap a little, which makes it harder to get even coverage. A 12-inch trowel is too long; when you're working in tight spaces (like between two walls), you'll bump into things.
The blade width also matters-standard is usually 5 to 6 inches. That width lets you hold enough mortar to do 2-3 bricks at a time, so you're not running back to the bucket every 30 seconds. I tried a 4-inch wide one once, and I felt like I was constantly reloading-it killed my momentum.
Now, there are smaller ones (8 inches) for detail work-like fixing a small section of a wall or working with thin bricks. And bigger ones (12 inches) for pros who lay bricks all day-they can handle the weight and speed. But for most people-beginners, DIYers, even casual pros-the 10-inch blade (5-6 inches wide) is the standard. I keep two trowels: a 10-inch for most jobs, and an 8-inch for touch-ups. That covers almost everything I need.
brick trowel from hanke tools
