How Big is a Spiral Staircase?

Floor to Floor Height

The first measurement you will need for your spiral staircase design is the floor to floor height. This is the total height of your spiral staircase from the bottom platform to the top of the design. You measure your floor to floor height by starting at the bottom floor where you plan to install the baseplate of your spiral staircase. While many people assume that you would simply measure floor to ceiling, this will result in your staircase being too short and create a large safety hazard for anyone using the stair. The proper way to measure your floor to floor height is to continue to measure through the floor of the above floor to the top of the floor. You have to factor in any underlayment, subflooring, carpeting, or tile that may add height on top of your standard floor. You want to be sure to measure to the height that your top platform will be flush against the floor. This ensures that your stair will be safe to use and stable.
floor to ceiling stair
Your floor to floor height will also affect some of your tread measurements. Your treads are the individual steps in your spiral staircase. The first tread measurement that will be dictated by your floor to floor height is the number of treads in your staircase. Once you know the number of treads that will be used in your design, you can then calculate your spiral stair’s rotation. Many people don’t realize that your stair may not reach a full 360 degree rotation. To meet building code, or a set of safety standards that you must meet to pass inspection, your treads have to have a 30 degree rotation. Therefore, if you have less than 12 treads, you will not have the full 360 degree rotation. A call to one of our consultative designers will help you to determine the right floor to floor height and the number of treads you will need for your spiral stair project.


A spiral staircase’s diameter is going to be one of the most important aspects of your design. Your stair’s width, or diameter, will be primarily determined by the size of the space where you are looking to put the staircase. While it may seem like spiral staircases are giant designs that take up a large portion of your floorplan, you can also design a spiral stair that can easily fit into a small corner out of the way. If you plan to tuck your spiral stair into a corner, the walls may define your diameter and frame the design. The smallest diameter that Salter Spiral Stair offers is a 3’6” staircase. This can easily fit into the small spaces and help you access previously hard to reach areas. Our diameters increase in 6” increments. From 3’6”, you can go up to a 4’, 4’6”, and so forth. If you want your stair to meet building code, you will need a minimum of a 5’ diameter for your spiral stair.

Another way to look at your diameter is to look at the footprint of your stair. The footprint is simply the amount of physical floor space that your stair will take up. This measurement takes the diameter, which is limited to the staircase itself, and applies it to your living space once the stair is installed. The beautiful thing about a spiral stair design is that the footprint is kept to a small circle in your floorplan. The best way to determine the right diameter for your space is to use the chart on our spiral staircase diameter and measurements page to find the footprint measurement. Use painters tape to tape off the potential footprint of your stair in your home. Once you’ve lived with the space taped off, you can adjust your design accordingly.

Your stair’s diameter will also determine your walking path. Your walking path is the amount of space that you will have to walk up and down your staircase. Because of the compact nature of a spiral stair design, many homeowners are concerned that there won’t be enough room to comfortably walk up and down your stair case. However, there is plenty of space to safely use your spiral stair on a regular basis. Our smallest diameter, 3’6” provides 17” of walking room. This number will increase by 3” for every 6” of diameter added to your design.

The last impact that your diameter will have is the well opening. This measurement will only apply to those installing their spiral stair through a hole in the floor. This measurement will be very close to your spiral stair’s diameter. However, we require that your well opening be at least 2” larger than your diameter. This is for the comfortable use of your handrail. Without the extra two inches, you will pinch your fingers moving up or down the space.

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