Ceiling Fan Size Calculator Match the Blade Span to the Room
Enter the room length and width. You get the recommended blade span and the airflow rating to look for on the box.
Floor Area Decides It
Blade span is chosen from the room's floor area, not from the ceiling height.
Check the CFM Too
Two fans of the same span can move very different amounts of air. The airflow rating is the honest number.
What size ceiling fan do I need?
At a Glance
Ceiling fans are sized by blade span — the diameter of the circle the blades sweep — and the span is chosen from the room's floor area. A small bedroom under 7 m² (75 ft²) wants roughly a 32 in / 80 cm fan; a 20 m² (215 ft²) living room wants about 47 in / 120 cm; anything over 37 m² (400 ft²) wants 54 in / 137 cm or more, or two smaller fans.
The published guidance is a set of area bands. Each band gives a span range rather than a single figure, because a fan one size either way still works — the calculator returns the midpoint of the band, which is the safe pick for the middle of the range.
| Room area | Blade span | Metric | Airflow (CFM) |
|---|---|---|---|
| up to 75 ft² / 7 m² | 29–36 in | 74–91 cm | ≥ 1,000 |
| up to 144 ft² / 13 m² | 36–42 in | 91–107 cm | ≥ 1,500 |
| up to 225 ft² / 21 m² | 44–50 in | 112–127 cm | ≥ 3,000 |
| up to 400 ft² / 37 m² | 50–54 in | 127–137 cm | ≥ 4,000 |
| over 400 ft² / 37 m² | 54–72 in | 137–183 cm | ≥ 6,000 |
The second column is the one people shop by; the fourth is the one that decides whether the fan actually cools the room. CFM — cubic feet per minute — is the volume of air the fan moves at top speed, and manufacturers selling into the US market have to publish it. A cheap 52 in fan might manage 3,000 CFM where a good one of the same size does 6,000.
area = length × width → look up the band → span = midpoint of the bandThese are the values the calculator loads by default.
Measure the floor
5 m × 4 m = 20 m².
Convert to square feet
The sizing bands are published in square feet: 20 × 10.764 = 215 ft².
Find the band
215 ft² falls in the "up to 225 ft²" band, which calls for a 44–50 in span and at least 3,000 CFM.
Take the midpoint
(44 + 50) ÷ 2 = 47 in = 119.4 cm. In practice you would buy the 120 cm fan on the shelf — that is what the sizing is for.
The span is a starting point, and three things move you off it.
High ceilings ask for more airflow, not a wider fan. The bands assume a standard ceiling around 2.4–2.7 m. Above that, keep the span and choose a fan with a higher CFM rating, hung on a downrod so the blades sit roughly 2.4 m above the floor. A fan flush against a 3.5 m ceiling stirs the air near the ceiling and not much else.
Long rooms want two fans, not one huge one. Once a room runs past about 5–6 m in its long direction, a single fan leaves the far end still. Two fans sized for half the room each, spaced evenly, beat one oversized fan.
Blades need clearance. Building guidance puts the blade tips at least 45–60 cm from the nearest wall or sloped ceiling, and the blades at least 2.1 m above the floor. If the recommended span does not fit that clearance, drop to the next size down.
For the cooling load itself — the number that decides an air conditioner rather than a fan — see the Air Conditioner BTU Calculator.
A rectangular-room rule of thumb
This calculator multiplies length by width, so it assumes a broadly rectangular room with one fan in the middle. L-shaped rooms, open-plan spaces and rooms with a sloped ceiling need judgement: size the fan for the part it hangs over, or split the space and use two.
The area bands themselves are industry guidance, not a standard with tolerances — different manufacturers publish charts that differ by an inch or two at the boundaries. Nothing bad happens if you land one size either way. Fans also do not lower the air temperature; they make a room feel a few degrees cooler while you are in the airflow, which is why turning one off in an empty room saves electricity and turning off an air conditioner does not.