I want to buy miniblinds. My windows are 29.75" wide. What size blind should I buy? I want to mount them on the inside.

If the inside of your window frame is 29 3/4 " wide, then I'd recommend getting a 28" or 28 1/2" blind as it won't hurt you to have about a one-inch gap on either end of the shades for movement and ease of opening/closing. With the goal of mounting them centered on your frame, you'll have very little sunlight exposure on the ends and your privacy will be ensured. If keeping out all sunlight is a priority, you might want to get some partial curtains to hang down on the ends of the blinds along the window frame. 29" would be ideally perfect, but realize that you'll need to get them mounted almost perfectly centered to allow a very modest gap on both ends. You want to avoid getting blinds so wide that one or both ends rub on the inside of the window box, as they'll scratch your paint or leave stains over time when being raised or lowered. One question......DO YOU OWN ANY INSIDE CATS? If so, I'm sure you're aware that a common habit for cats is lounging in the window sill, and I learned the hard way that buying the plastic or aluminum "mini" blinds is a huge mistake. Cats like to paw and play with them, and in no time they'll be bent or broken. I opted for the 2" plastic slats with the set I bought, and although they're much more expensive, they're worth it with their superior durability. They also look quite attractive. Good luck to you!