With blinds, one of your first decisions is whether to mount your blinds inside or outside the window. If you do not want to have a light gap, outside mount blinds are the better choice.

Inside mount blinds, which mount inside of your window's case, look neater. But you will always have at least a little light gap of between 3/16 inch and 3/4 inch on each side. Inside mount blinds are ordered using the actual window opening width (smallest of the measurements at the top, middle & bottom of the window). The factory then makes the width at a smaller size (deduction varies by product and is listed on the specification page on each product on our site) so the blinds will fit inside the window and move freely. So, all inside mount blinds/shades have gaps on each side. Cellular shades and roman shades usually have the smallest width deductions.

Outside mount blinds will block light better than inside mount blinds because they can cover the entire window opening. You need to make sure to add at least 2 inches to your window opening width measurement and at least 3 inches to the window opening height measurement to get the best coverage. Even when you add to the width and height measurements there may still be some light leakage around the edges. However, when the fabric is 100% blackout, outside mount blinds will block approximately 99.9% of all light. With outside mount blinds, you have a few options for total blackout:

1. Single-cell/double-cell blackout cellular shades – We have single cell blackout honeycomb fabrics and double-cell blackout shades that work very well. The fabric for both of these shades will block 100% of light. Be sure to add to your width and height measurements.
2. Blackout roller shades – Roller shades are also available in 100% blackout fabrics. However, you have to make sure to add at least 3 inches to both your width and height window measurements. Roller shades are ordered using the width at the top of the shade. The top of a roller shade will be 7/8 inches to 1 1/2 inches wider than the fabric (varies by factory, fabric deductions are listed on the specification page on each product on our site). Our customer service team can help you make these measurements accurately if you have questions. Also, remember we have a "Fit or Free Guarantee." That means that if you make a mistake when measuring, we'll remake your blinds at no charge. All you pay for is the price difference (if any), and shipping. Learn more about our Blackout roller shades.
3. We even have a combination shade called a Deluxe Cordless Day/Night Single Cellular Shade that has a light filtering shade at the top and blackout shade at the bottom. You can then use the light filtering fabrics when you want light and the blackout fabric when you want to darken the room.
4. You can get a blackout option with just about any of our shades – we're not joking around here. Most of our products (i.e., roman shades, bamboo shades, etc.) can be ordered with a blackout liner. You can check out the total selection of blackout shades here. However, these products still have a light gap on either side so to get the best coverage add the 2 to 3 inches to the width and height measurement of your window opening and mount outside the window.

And remember we have a 60-Day Satisfaction Guarantee in place to protect you. So if you don't like your blinds for any reason, we'll do whatever we can to make you happy, or you get a refund. And if you do return your blinds, you can feel good about it because all returned blinds get donated to a local charity.