The cost of interior design depends on a number of factors, including the size of the space, the scope of the project, the materials used, and the designer's experience. Generally, designers charge an hourly fee for their services, which can range from $50 to $200 per hour. Some designers may also charge a flat fee or a percentage of the total project cost. Additionally, the cost of materials and furnishings must also be considered when calculating the cost of interior design.