Measure your room length and width first
The size of your ceiling fan must match the size of your room. A fan that is too small will not circulate air effectively; a fan that is too large will look out of proportion and waste energy. Start by measuring the length and width of the room in feet using a tape measure. Multiply these two numbers together to get the square footage of the room.
Once you have the square footage, use this standard guide: rooms under 75 square feet need a fan with a 29-inch blade span; rooms from 75 to 144 square feet need 36 inches; rooms from 144 to 225 square feet need 42 inches; rooms from 225 to 400 square feet need 52 inches; rooms over 400 square feet need 56 inches or larger, or two fans. A blade span is the distance from the tip of one blade to the tip of the opposite blade when the blades are fully extended.
Key Takeaways
- Multiply your room's length by its width to find square footage, then match that to the correct blade span using the standard sizing chart.
- Measure the distance from the floor to your ceiling to may support the fan hangs at least 7 feet above the floor and 10 inches below the ceiling.
- Check the width of your mounting bracket against the width of your ceiling joist or electrical box to confirm the fan will attach securely.
- Measure the distance from the ceiling to any obstacles like light fixtures, walls, or beams to make sure the blades will have clearance to spin freely.
- If your ceiling is sloped or vaulted, use an angled mounting bracket and measure the angle of the slope with a digital level.
Check the height from floor to ceiling
The fan must hang at a safe distance from the floor and from the ceiling. Measure the distance from the floor to your ceiling in feet and inches. The bottom of the fan blades should be at least 7 feet above the floor — this is the minimum clearance to avoid hitting people's heads. The top of the fan motor should be at least 10 inches below the ceiling to allow heat to escape and to prevent the blades from hitting the ceiling if they wobble.
If your ceiling is 8 feet tall, the fan will fit with room to spare. If your ceiling is lower than 8 feet, you will need a flush-mount fan, which sits directly against the ceiling with no downrod (the metal rod that hangs the motor). If your ceiling is higher than 9 feet, you can use a standard downrod, but you may want a longer one to keep the blades in the middle of the room rather than too high up.
Measure your mounting location and joist spacing
Ceiling fans must be attached to a joist — a wooden beam that runs across the ceiling — or to an electrical box rated for fan weight. Do not attach a fan to drywall alone. Use a stud finder to locate the joists in your ceiling. Joists in most homes are spaced 16 inches apart, measured from the center of one joist to the center of the next.
Measure the width of your fan's mounting bracket. Most brackets are 4 to 6 inches wide. If your bracket is wider than the distance between joists, you will need to install a fan-rated electrical box that spans between two joists. These boxes are sold at hardware stores and come with instructions for installation. Measure the distance from the center of one joist to the center of the next to confirm your bracket will fit, or to know what size box you need to buy.
Account for obstacles and blade clearance
The blades must spin without hitting walls, light fixtures, beams, or other objects. Measure the distance from the center of the fan to the nearest wall, corner, or obstacle in all directions. Each blade tip should be at least 18 inches away from any wall or obstacle. If your room has a sloped ceiling, a beam, or a light fixture near where you want to mount the fan, you may need to move the fan to a different location or choose a smaller blade span.
If you are mounting the fan in a corner or near a wall, measure carefully. A 52-inch fan has blades that extend 26 inches from the center in each direction, so it needs a space at least 52 inches wide and 52 inches deep to spin freely. Smaller rooms may require a 36-inch or 42-inch fan instead.
Measure ceiling slope for angled mounting
If your ceiling is sloped or vaulted, you cannot use a standard downrod. Measure the angle of the slope using a digital level — a tool that displays the angle in degrees. Place the level against the ceiling and read the angle. Most angled mounting brackets work for slopes up to 45 degrees.
Write down the angle and bring it with you when you shop for a fan. The fan's downrod will need to be angled to match the ceiling slope. Some fans come with an angled bracket in the box; others require you to buy one separately. Measure the length of the downrod you need by measuring from the ceiling to where you want the fan motor to hang, then add 2 inches for the bracket connections.
Verify electrical box depth and wiring access
The electrical box where the fan will mount must be deep enough to hold the fan's mounting bracket and wiring. Measure the depth of your existing electrical box — the distance from the front of the box to the back where it meets the joist. Most fan boxes are 2 to 3 inches deep. If your box is shallower than 2 inches, you will need to replace it with a fan-rated box.
Also measure the distance from the electrical box to the nearest light switch or wall outlet. You will need to run a wire from the box to a switch if one does not already exist. If the switch is more than 10 feet away, you may want to install a new switch closer to the fan location, or use a remote-control fan instead. Measure the path the wire will take — along the joist, through the attic, or down the wall — to know how much wire you will need to buy.
Create a measurement checklist before you buy
Write down all your measurements on a piece of paper or take photos with your phone before you go to the store. Include the room's square footage, the height from floor to ceiling, the type of mounting you need (standard, flush, or angled), the angle of any slope, the joist spacing, the distance to obstacles, and the depth of your electrical box. Bring this information with you when you shop, or show it to a sales associate at the store.
Having all your measurements in one place will help you choose a fan that fits your space and will make installation easier. If you are unsure about any measurement, take it twice to confirm. A fan that is the wrong size or mounted incorrectly will not work well and may be unsafe.
Frequently Asked Questions
What if my ceiling is too low for a standard ceiling fan?
Use a flush-mount fan, which attaches directly to the ceiling with no downrod. These fans sit only 4 to 6 inches below the ceiling. They work best in rooms under 144 square feet. If your ceiling is lower than 7 feet 6 inches, a flush-mount fan is your only option.
Can I mount a ceiling fan on drywall without a joist?
No. Drywall alone cannot support the weight and vibration of a ceiling fan. You must attach the fan to a joist or to a fan-rated electrical box that is bolted between two joists. Installing a fan on drywall is a safety hazard and may cause the fan to fall.
How do I know if my electrical box is rated for a ceiling fan?
Look for a label on the box that says "fan-rated" or "fan support." Standard electrical boxes are not strong enough. If your box is not labeled, assume it is not fan-rated and replace it with one that is. Fan-rated boxes are sold at hardware stores and cost between $15 and $40.
What blade span do I need for a bedroom that is 12 feet by 14 feet?
Multiply 12 by 14 to get 168 square feet. A room of 168 square feet needs a fan with a 42-inch blade span. A 36-inch fan would be too small and would not circulate air well; a 52-inch fan would be too large for the space.
Do I need to measure anything if I am replacing an existing ceiling fan?
You should still measure your room's square footage to confirm the old fan was the right size. If the old fan did not circulate air well or looked too small or too large, use your measurements to choose a better size. Also measure the height from floor to ceiling to confirm a flush-mount or standard fan will work in your space.