🌀CFM, m³/h, litres per second — the same air

✓ Tested & verified Updated: Aug 9, 2026 How we calculate this

Airflow converter

Airflow

Given in

100 CFM = 170 m³/h

= 47.2 litres per second · 0.047 m³/s

Typical rating	CFM	m³/h	L/s
Bathroom fan	50	85	24
Bathroom fan	80	136	38
Bathroom fan	100	170	47
Ceiling or inline fan	150	255	71
Ceiling or inline fan	200	340	94
Range hood	400	680	189
Range hood	600	1,019	283
Whole-house or duct trunk	1,200	2,039	566
Whole-house or duct trunk	2,000	3,398	944

Ventilation standards are written in litres per second per person; fans are sold in CFM or m³/h. This is the line between the two.

Try also

How do you convert CFM to m³/h?

Multiply CFM by 1.699 to get cubic metres per hour. Go the other way by dividing. For litres per second, multiply CFM by 0.472 — or, close enough for choosing a fan, halve it.

The reason four units exist for one quantity is that four different trades wrote them down. CFM — cubic feet per minute — is what North American fans and hoods are rated in. m³/h is what European extractor fans and air handlers carry on the label. Litres per second is the unit ventilation standards are written in, because requirements are per person and per second is the human scale. m³/s turns up in engineering calculations and almost nowhere else, because ordinary house numbers come out as fractions of one.

A useful anchor: 100 CFM ≈ 170 m³/h ≈ 47 L/s. That is a typical bathroom extractor, and once you know that one line, the rest of the range is easy to place.

The conversions in one line each, for the times you want the number without the calculator.

From	To	Multiply by
CFM	m³/h	1.699
CFM	L/s	0.472
m³/h	CFM	0.5886
m³/h	L/s	0.2778
L/s	CFM	2.119
L/s	m³/h	3.6

The last row is the one worth memorising, because it is exact: a litre per second is 3.6 cubic metres an hour, and that falls straight out of 3,600 seconds in an hour and 1,000 litres in a cubic metre. No approximation involved.

Frequently asked questions

What is 100 CFM in m³/h?

About 170 m³/h — 169.9 to be exact. That is the size of a normal bathroom extractor fan, which is why the two figures 100 and 170 turn up so often on the same shelf: they are the same fan sold into two markets.

How do I convert CFM to litres per second?

Multiply by 0.472. In practice, halving the CFM gets you within 6%, which is close enough to check whether a fan meets a ventilation requirement written in L/s. Going the other way, double the L/s figure and take a little off.

Why are ventilation rules written in litres per second?

Because the requirement is per person and per second — typically 8 to 10 L/s of fresh air per person for an office. Those are small, human-sized numbers. The same rule in CFM would be 17 to 21 CFM per person, and in m³/h it would be 29 to 36, neither of which is easier to remember.

Is CFM the same as air changes per hour?

No, and it is the most common mix-up. CFM is a rate of flow; air changes per hour is that rate compared with the size of the room. The same 100 CFM fan gives 6 air changes an hour in a small bathroom and less than one in a living room. Convert with ACH = CFM × 60 ÷ room volume in cubic feet.

What CFM is a range hood usually?

Between 200 and 600 CFM for a domestic hood, which is 340 to 1,020 m³/h. Island hoods sit at the top of that range because they have no walls to help contain the plume. Anything over about 400 CFM in a tightly sealed house needs make-up air, or the hood will pull it down the flue of whatever else is burning.

How much air does a whole house need?

As a rule of thumb, 0.35 air changes an hour, or 15 CFM per person, whichever is greater — that is the long-standing ASHRAE residential baseline. A 2,000 sq ft house with 8 ft ceilings is 16,000 cubic feet, so about 93 CFM, or 160 m³/h, running continuously.

How we calculate this

Conversions are exact, based on the definitions of the foot and the metre: one cubic foot is 0.028316846592 m³, so 1 CFM = 1.699011 m³/h = 0.4719474 L/s = 0.0004719474 m³/s. Everything is computed through CFM as the base unit so that rounding is applied once, at display, rather than compounding through a chain of conversions. The typical equipment ratings in the table are the ranges these products are commonly sold in, not a standard; the 0.35 air changes per hour and 15 CFM per person residential ventilation baseline is from ASHRAE Standard 62.2.

Worked example

With Airflow 100, Given in CFM — cubic feet per minute, this page works out 100 CFM = 170 m³/h. = 47.2 litres per second · 0.047 m³/s

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