A standard 3/8 inch deduction is made to the upper rail width for a proper inside mount fit. The actual blind size will be 19 5/8" W x 48" H, perfect for window 20" W x 48" H. The unique spring rod can extend 1 inch in total, allow the blind to fit for window size W 19.7-20.6 X H 48". No Drill Blinds: LazBlinds patented technology No Tools-No Drill system allow it no need to drill any holes on your window frame. Perfect for Renter, Landlord, and Home Buyer. Easy to Install in 30 seconds without screws or brackets. Fit All Kinds of Walls, like woodiness metope, tile marble, concrete wall and rough tile. Privacy Blinds for Windows: Premium dense S-curve slats with invisble hole design can completely keep out the sunlight and uv ray, offering a real dark environment. At the same time it is possible to use the twisting wand to switch between light filtering or room darkening. Perfect for living room, family room, bedroom, bathroom. Cordless Blinds for Windows: No more exposed dangling cords. Providing a more modern and cleaner appearance to every room and a safe environment for home with pets and kids. Simply hold the bottom rail to lift or lower the blind down. If you have difficulties in choosing the size or if there are any quality problems or missing accessories after receiving the parcel, pls contact us directly and we will re-send it to you. We can also make custom sizes, any questions please feel free to contact us: CustomerService@coprisma.com.