To measure the bed accurately, it is important that you strip the bed of all bedding. Use a retractable measuring tape. Place one end of the measuring tape at the left side of the bed and now pull the tape out till it reaches the right edge of the bed. Note down its measurement. Now place the measuring tape in the centre of the bed and pull it down from the top to the bottom and note down its measurement. These measurements will help in determining the size of the bed.