Cubic Feet Per Minute To Cubic Metres Per Hour Converter
Convert airflow between CFM and m3/h for fans, ventilation schedules, extraction rates and HVAC notes, with optional quantity and room air-change checks.
Airflow Inputs
Converted Airflow
This is a volume flow conversion. It does not adjust for fan pressure, duct losses, temperature, altitude or measured air density.
What This Converter Is For
Fan catalogues, data sheets and ventilation discussions often switch between cubic feet per minute and cubic metres per hour. CFM is common in North American fan ratings, while m3/h is common in UK and European ventilation documents. This page converts the unit and lets you scale the result for several identical fans or terminals.
The optional air-change line uses room volume to estimate ACH, or air changes per hour. That can help with a quick sense check, but it is not a substitute for a ventilation design. Real flow depends on duct length, bends, grilles, filters, pressure drop, commissioning and whether the fan actually reaches its rated point.
Formula
1 cubic foot = 0.028316846592 cubic metres1 minute = 1/60 hour1 CFM = 0.028316846592 x 60 = 1.69901079552 m3/hm3/h = CFM x 1.69901079552CFM = m3/h / 1.69901079552The factor is based on exact length conversion between foot and metre. Rounding in catalogues can create small differences, especially when values are shown as whole numbers.
Quick Conversion Table
| CFM | m3/h | Typical note |
|---|---|---|
| 25 | 42.48 | Small local extract or component airflow. |
| 50 | 84.95 | Small fan rating. |
| 75 | 127.43 | Domestic ventilation comparison. |
| 100 | 169.90 | Easy anchor value. |
| 150 | 254.85 | Kitchen or utility extract example. |
| 250 | 424.75 | Larger fan or several terminals. |
| 500 | 849.51 | Commercial airflow example. |
Worked Examples
Single Fan
A fan rated at 100 CFM converts to 169.90 m3/h. If the catalogue rounds to 170 m3/h, the difference is ordinary display rounding.
Two Identical Fans
Two 75 CFM fans provide a catalogue total of 150 CFM, equal to about 254.85 m3/h before duct losses or balancing.
Room ACH Check
169.90 m3/h in a 30 m3 room is about 5.66 air changes per hour if that airflow is actually delivered.
Using CFM And m3/h In Practice
Use this conversion when matching a fan rating to a specification, translating a product manual, preparing a schedule or checking a quote. Keep the original value visible where possible. If a fan curve gives airflow at different pressures, convert the airflow at the design pressure, not only the free-air headline value.
For commissioning, measured airflow may be reported in litres per second, m3/h or CFM. Convert all readings to one unit before comparing them with the design schedule. If the measured value is low, the reason is usually a system issue rather than a unit conversion issue.
Room Volume And ACH Notes
The ACH line divides delivered m3/h by the room volume entered. It is a quick arithmetic check, not a design target. A bathroom, kitchen, classroom, workshop and plant room can all need different ventilation approaches. Some spaces are designed by extract rate, some by outdoor air per person, some by heat load and some by process requirement. If a regulation, standard or employer specification gives a target, use that document first and use this page only to put the units into the same form.
Room volume also needs care. Measure the internal floor area and clear height where air can move. Do not include loft voids, boxed-in risers or neighbouring rooms unless the ventilation design actually connects them. For open-plan spaces, use the volume served by the fan or air terminal, not the whole building.
Fan Rating Checks
A product may show a free-air rating, a tested rating through a standard duct, or a full fan curve. Free-air figures are often higher than installed performance because they assume little resistance. Filters, grilles, non-return flaps, flexible duct, long runs and sharp bends can lower delivered flow. When comparing quotes, ask whether the figure is catalogue airflow, design airflow or commissioned airflow. The unit conversion is exact, but the source value may not describe the installed system.
For a report, write both units once and then use one unit consistently. That makes later checking easier for installers, clients and maintenance teams.
Common Mistakes To Avoid
- Confusing m3/h with m3/s; they differ by a factor of 3,600.
- Adding fan ratings without considering duct pressure and controls.
- Using free-air fan ratings as installed airflow.
- Forgetting that several terminals may share one fan.
- Rounding too early in a design spreadsheet.
FAQs
How many m3/h is 1 CFM?
1 CFM is 1.69901079552 m3/h.
How do I convert m3/h to CFM?
Divide m3/h by 1.69901079552.
Is this the same as m3/s?
No. m3/h and m3/s are different flow units. m3/s is much larger for the same number.
Does the conversion include duct losses?
No. It is a pure unit conversion. Duct losses affect delivered airflow, not the conversion factor.
Can I use it for water flow?
The volume unit conversion is mathematically valid, but CFM is most often used for air. Use a flow tool suited to the fluid and context.
Sources
- National Institute of Standards and Technology. (2008). Guide for the Use of the International System of Units (SI), Special Publication 811. NIST. https://www.nist.gov/pml/special-publication-811
- Bureau International des Poids et Mesures. (2019). The International System of Units (SI), 9th edition. BIPM. https://www.bipm.org/en/publications/si-brochure
- ASHRAE. (2024). ASHRAE Handbook: HVAC Applications. American Society of Heating, Refrigerating and Air-Conditioning Engineers.
- CIBSE. (2023). Guide B: Heating, ventilating, air conditioning and refrigeration. Chartered Institution of Building Services Engineers.