Need to compare a US‑based flow spec with a metric one? Converting cubic feet per minute (ft³/min) to litres per day (L/d) can feel like translating two different languages. This guide breaks the math down, shows why the conversion matters, and gives you ready‑to‑use numbers so you never have to guess again.
Volume Flow Rate: The Measure That Connects the Units
Volume flow rate tells us how much space‑filling material passes a point in a given time. Whether you’re moving air, water, or oil, the underlying concept stays the same: volume ÷ time.
What Is a Cubic Foot Per Minute (ft³/min)?
A cubic foot is the volume of a cube 1 ft on each side. When we say “per minute,” we’re measuring how many of those cubes flow past each second in one minute. It’s a common unit in HVAC, gas pipelines, and US‑based industrial equipment.
What Is a Litre Per Day (L/d)?
A litre is the metric volume equal to one‑cubic‑decimetre. “Per day” stretches the time frame to 24 hours, a natural choice for water‑treatment plants, chemical dosing, and long‑term process monitoring.
Exact Conversion Factor
The relationship is fixed by two well‑known constants:
- 1 ft³ = 28.316846592 L
- 1 day = 1,440 minutes
Multiplying them gives the precise factor:
1 ft³/min = 40,776.2591 L/d
How to Convert – The Simple Formula
Take the flow value in ft³/min and multiply by the factor above.
Litres per day = (Cubic feet per minute) × 40,776.2591
That’s it. No extra steps, no hidden tricks.
Worked Example: From Airflow to Daily Volume
Imagine an HVAC fan rated at 3 ft³/min. How many litres does it move in a full day?
- Identify the source value: 3 ft³/min.
- Apply the formula: 3 × 40,776.2591 = 122,328.7773 L/d.
- Round for readability (optional): ≈ 122,329 L/d.
The fan pushes roughly 122 kL of air every 24 hours.
Why This Conversion Matters in Real Life
- HVAC design: US‑spec equipment often lists airflow in ft³/min, while energy‑efficiency standards may require metric reporting.
- Water‑treatment facilities: Pumps sized in US units need to be compared with daily dosing schedules expressed in litres.
- Process engineering: Chemical reactors may be rated in ft³/min, yet inventory calculations use L/d for safety documentation.
- Regulatory compliance: Many environmental permits demand daily volume disclosures in litres, regardless of the original measurement system.
Cubic Foot Per Minute to Litre Per Day Conversion Table
Each row applies the same rule: multiply cubic feet per minute by 40,776.2591.
| Cubic Foot Per Minute (ft³/min) | Litre Per Day (L/d) |
|---|---|
| 1 ft³/min | 40,776.2591 L/d |
| 2 ft³/min | 81,552.5182 L/d |
| 5 ft³/min | 203,881.2955 L/d |
| 10 ft³/min | 407,762.5910 L/d |
| 20 ft³/min | 815,525.1820 L/d |
| 50 ft³/min | 2,038,812.9550 L/d |
| 100 ft³/min | 4,077,625.9100 L/d |
| 500 ft³/min | 20,388,129.5500 L/d |
Bottom Line
One cubic foot per minute equals 40,776.2591 litres per day. Multiply any ft³/min value by this factor and you have an instant, accurate metric flow rate. Use the table for quick look‑ups, and apply the formula whenever you need a custom number.
Ready to streamline your calculations? Plug the factor into your spreadsheets, reports, or design software and let the numbers do the heavy lifting.