Bundt cakes are one situation where you want to get this right. Too little batter, and your cake can look like an oversized donut. Too much can lead to an epic mess in your oven. For best results, fill your pan about two-thirds of the way to the top. If you’re not using a recipe specifically for bundt cakes, look for one used to make a single 9” x 13” rectangular cake or two 9” round pans. If you’re making angel food or a similar eggwhite-based batter cake, allow room for it to rise a lot. If you’re worried about spillover during baking, put the bundt pan on or over a large sheet pan, so it catches any spillage (versus the bottom of your oven, which will create a big mess to scrub, not to;mention a smoke/fire hazard).