💧 Flow Rate Conversion Calculator
Convert between Volume Flow, Mass Flow & Molar Flow — L/min, GPM, m³/h, CFM, kg/s, mol/s, and 60+ more units
🔄 Flow Rate Converter
📊 All Conversions at Once
📖 How to Use the Flow Rate Converter
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1Select the Flow Type
Click one of the three tabs — Volume Flow, Mass Flow, or Molar Flow — to load the relevant unit list. Volume flow is for liquids in pipes; mass flow is preferred for gases and chemical processes; molar flow is used in chemistry and reaction engineering.
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2Enter Your Value
Type the numerical flow rate you want to convert into the "Enter Value" field. Decimals and scientific notation are supported (e.g., 1.5e4 for 15,000). The converter updates instantly as you type.
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3Choose From & To Units
Select your source unit from the "From Unit" dropdown and the target unit from "To Unit". The result and the exact conversion formula used are shown immediately in the result panel.
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4View All Conversions
The "All Conversions at Once" panel automatically converts your input to every unit in the current category — ideal for creating quick reference tables on the spot.
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5Swap Direction with One Click
Hit the ⇄ button to instantly reverse the conversion direction — swapping From and To units — without re-entering data.
📐 Common Flow Rate Conversion Table
| From | To | Multiply By | Formula (Math) |
|---|---|---|---|
| L/min | gpm (US) | × 0.26417 | \( Q_{\text{gpm}} = \dfrac{Q_{\text{L/min}}}{3.7854} \) |
| gpm (US) | L/min | × 3.7854 | \( Q_{\text{L/min}} = Q_{\text{gpm}} \times 3.7854 \) |
| m³/h | L/min | × 16.667 | \( Q_{\text{L/min}} = Q_{\text{m³/h}} \times \dfrac{1000}{60} \) |
| m³/h | gpm (US) | × 4.4029 | \( Q_{\text{gpm}} = Q_{\text{m³/h}} \times 4.4029 \) |
| CFM (ft³/min) | L/min | × 28.317 | \( Q_{\text{L/min}} = Q_{\text{CFM}} \times 28.317 \) |
| L/s | m³/h | × 3.6 | \( Q_{\text{m³/h}} = Q_{\text{L/s}} \times 3.6 \) |
| kg/s | lb/min | × 132.277 | \( \dot{m}_{\text{lb/min}} = \dot{m}_{\text{kg/s}} \times 132.277 \) |
| kg/h | lb/h | × 2.2046 | \( \dot{m}_{\text{lb/h}} = \dot{m}_{\text{kg/h}} \times 2.2046 \) |
| bbl/day | L/min | × 0.11042 | \( Q_{\text{L/min}} = Q_{\text{bbl/day}} \times 0.11042 \) |
🔬 Understanding Flow Rate — A Complete Guide
Flow rate is one of the most critical measurement quantities in engineering, science, industry, and everyday infrastructure. Whether you are designing a water distribution system, specifying an HVAC duct, monitoring a chemical reactor, or setting irrigation schedules, flow rate is the central variable. Understanding the three types of flow rate — volume flow, mass flow, and molar flow — and knowing how to convert between their many units is an essential skill for students, engineers, and technicians worldwide.
At its most fundamental level, flow rate describes how much of something moves past a point per unit of time. The "something" can be a volume, a mass, or a number of moles of substance. Each measurement has advantages in different contexts.
📊 Volume Flow Rate — Qv
Volume flow rate \( Q_v \) (also written \( \dot{V} \)) is the volume of fluid that passes a given cross-section per unit time. It is the most commonly encountered form of flow rate for liquid applications such as water supply, plumbing, HVAC, irrigation, and industrial process lines.
The most commonly used unit in practice, however, is litres per minute (L/min) in metric countries and gallons per minute (GPM) in the United States. For large industrial and municipal systems, cubic metres per hour (m³/h) and cubic feet per minute (CFM) are standard.
The Continuity Equation (Flow from Velocity)
For a fluid flowing through a duct or pipe of cross-sectional area \(A\), the volume flow rate is related to the average fluid velocity \(v\) by the continuity equation:
Given: A water pipe with diameter 50 mm (radius 0.025 m) carries water at an average velocity of 2 m/s.
\[ Q_v = \pi \times (0.025)^2 \times 2 = \pi \times 6.25 \times 10^{-4} \times 2 \approx 3.927 \times 10^{-3}\,\text{m}^3/\text{s} \]
\[ Q_v = 3.927\,\text{L/s} = 235.6\,\text{L/min} = 62.24\,\text{gpm} \]
Answer: The pipe delivers approximately 235.6 L/min or 62.2 GPM (US).
⚖️ Mass Flow Rate — ṁ
Mass flow rate \( \dot{m} \) is the mass of substance passing a point per unit time. Unlike volume flow rate, mass flow rate is independent of temperature and pressure — it does not change when a gas expands or a liquid changes temperature. This makes it the preferred measurement in:
- Gas flow in compressors, turbines, and combustion systems
- Chemical process engineering and reactor design
- Food processing and pharmaceutical manufacturing
- HVAC psychrometric calculations (humid air handling)
- Fiscal gas metering (billing by mass is more accurate than by volume)
Given: Water (density \(\rho = 1{,}000\,\text{kg/m}^3\)) flows at \(Q_v = 10\,\text{L/min} = \frac{10}{1000 \times 60}\,\text{m}^3/\text{s} = 1.667 \times 10^{-4}\,\text{m}^3/\text{s}\).
\[ \dot{m} = \rho \times Q_v = 1{,}000 \times 1.667 \times 10^{-4} = 0.1667\,\text{kg/s} = 10\,\text{kg/min} \]
Answer: For water, 10 L/min = 10 kg/min (since water's density is 1 kg/L at standard conditions).
Given: An HVAC duct carries air (density \(\rho = 1.2\,\text{kg/m}^3\) at 20°C, 1 atm) at a volume flow of \(Q_v = 500\,\text{m}^3/\text{h}\).
\[ Q_v = \frac{500}{3600}\,\text{m}^3/\text{s} = 0.1389\,\text{m}^3/\text{s} \]
\[ \dot{m} = 1.2 \times 0.1389 = 0.1667\,\text{kg/s} = 600\,\text{kg/h} \]
Answer: The duct delivers 600 kg/h of air. Unlike volume flow, this won't change if the air density changes at different floor levels of a building.
🔬 Molar Flow Rate — ṅ
Molar flow rate \( \dot{n} \) (sometimes written \( F \) or \( \dot{N} \)) is the number of moles of a substance passing a point per unit time. It is the fundamental unit of flow in chemical reaction engineering, because stoichiometry — the study of how chemicals react in proportion — is expressed in moles, not kilograms or litres.
Given: Pure nitrogen (N₂, molar mass \(M = 28.014\,\text{g/mol}\)) flows at a mass flow rate of \(\dot{m} = 5\,\text{kg/h}\).
\[ \dot{m} = \frac{5}{3600}\,\text{kg/s} = 1.389 \times 10^{-3}\,\text{kg/s} \]
\[ \dot{n} = \frac{\dot{m}}{M} = \frac{1.389 \times 10^{-3}}{0.028014} \approx 0.04958\,\text{mol/s} = 178.5\,\text{mol/h} \]
Answer: 178.5 mol/h of nitrogen — useful for sizing a reactor or determining reaction rates stoichiometrically.
🔗 Key Relationships Between Flow Rate Types
The three flow rate types are related through two material properties: the fluid's density \(\rho\) and its molar mass \(M\). This triangle of relationships allows engineers to translate between all three measurement systems:
Volume → Mass Flow
Multiply by density: \( \dot{m} = \rho \times Q_v \)
For water at 25°C: \(\rho \approx 997\,\text{kg/m}^3\) (nearly 1 kg/L)
Mass → Molar Flow
Divide by molar mass: \( \dot{n} = \dot{m} / M \)
E.g., water (M = 18.015 g/mol): 18.015 g/s = 1 mol/s
Molar → Volume Flow
Multiply by molar volume: \( Q_v = \dot{n} \times V_m \)
Ideal gas at STP: \( V_m = 22.414\,\text{L/mol} \)
Temperature & Pressure Effects
Volume flow changes with T & P via the ideal gas law: \( Q_{v2} = Q_{v1} \times \frac{T_2 P_1}{T_1 P_2} \). Mass and molar flow remain constant.
📋 Important Flow Rate Units Explained
GPM — Gallons Per Minute
GPM (US gallons per minute) is the dominant volume flow unit in the United States for plumbing, irrigation, fire suppression, and pump specifications. One US gallon equals exactly 3.785411784 litres. A typical residential shower uses 1.8–2.5 GPM; a fire hydrant flows at 500–1,500 GPM; a large municipal water pump may deliver 10,000–50,000 GPM.
Important: The UK Imperial gallon (4.54609 L) is larger than the US gallon. Specification sheets from British manufacturers use UK GPM, which produces values about 17% lower than US GPM for the same physical flow. Always verify which gallon is intended.
CFM — Cubic Feet per Minute
CFM (cubic feet per minute) is the standard air flow measurement in US HVAC and ventilation engineering. Residential air handlers are sized in CFM (typically 400 CFM per ton of cooling capacity); industrial dust collectors, spray booths, and clean rooms are all rated in CFM. The conversion is: \[ 1\,\text{CFM} = 28.3168\,\text{L/min} = 0.4719\,\text{L/s} \] SCFM (Standard CFM) corrects airflow to standard conditions (68°F / 20°C, 1 atm), making valid comparisons between systems operating at different temperatures and altitudes.
bbl/day — Barrels per Day (Petroleum)
In the oil and gas industry, production and refinery throughput are universally reported in barrels per day (bbl/day or B/D). A petroleum barrel is exactly 42 US gallons = 158.987 litres. Global oil production is approximately 100 million barrels per day. The conversion to more familiar units: \[ 1\,\text{bbl/day} = \frac{158.987\,\text{L}}{86{,}400\,\text{s}} \approx 1.84 \times 10^{-3}\,\text{L/s} \approx 0.11042\,\text{L/min} \]
Standard vs. Normal Volume Flow (SCFM, Nm³/h)
Gas volume flow is highly dependent on temperature and pressure. To allow meaningful comparison between systems at different conditions, the gas industry uses standardised reference conditions:
- Standard conditions (US): 60°F (15.56°C) and 14.696 psia (1 atm) → used for SCFM, SCFD
- Normal conditions (European): 0°C and 101.325 kPa → used for Nm³/h, NL/min
To convert actual volume flow to standard conditions using the ideal gas law: \[ Q_{\text{std}} = Q_{\text{actual}} \times \frac{T_{\text{std}}}{T_{\text{actual}}} \times \frac{P_{\text{actual}}}{P_{\text{std}}} \] where temperatures must be in Kelvin and pressures in the same unit (e.g., Pa or psia).
⚙️ How Flow Rate is Measured — Instrument Overview
Accurate flow measurement is critical in process control, billing, environmental monitoring, and safety. The choice of flowmeter depends on the fluid type, required accuracy, pipe size, temperature/pressure range, and budget. Key measurement technologies include:
- Differential pressure (DP) meters (orifice plate, venturi, flow nozzle): Measure pressure drop across a constriction. Volume flow is derived via Bernoulli's equation: \( Q_v = C_d \cdot A \cdot \sqrt{\dfrac{2\Delta P}{\rho}} \), where \(C_d\) is the discharge coefficient.
- Turbine flowmeters: A rotor spins proportionally to flow rate. High accuracy (±0.1–0.5%) for clean liquids. Pulse output directly in L/min or GPM.
- Electromagnetic (mag) flowmeters: Based on Faraday's law — a voltmeter measures the EMF induced by conductive fluid moving through a magnetic field. Works only with electrically conductive liquids. Excellent for slurries and corrosive fluids.
- Coriolis mass flowmeters: One of the most accurate instruments available (±0.1–0.2%). Measures mass flow directly by sensing the Coriolis force induced on a vibrating tube. Widely used in the pharmaceutical, food, and chemical industries.
- Ultrasonic flowmeters: Measure the transit-time difference of sound pulses travelling upstream vs. downstream. Non-invasive (clamp-on) versions are used for retrofitting without pipe interruption.
- Rotameters (variable-area meters): A float rises in a tapered tube proportional to flow. Simple, inexpensive, and widely used for local indication in labs and process plants.
📊 Flow Rate Reference Table by Application
| Application | Typical Flow Rate | Unit | Equivalent |
|---|---|---|---|
| Dripping faucet | ~0.1 | L/min | 0.026 GPM |
| Shower head (efficient) | 6–8 | L/min | 1.6–2.1 GPM |
| Garden hose (full) | 30–45 | L/min | 8–12 GPM |
| Residential HVAC air handler | 400–800 | CFM | 680–1360 m³/h |
| Industrial pump (medium) | 200–2,000 | m³/h | 880–8,800 GPM |
| Natural gas pipeline (main) | 10–100 | MMscfd | 10⁶–10⁷ Nm³/day |
| Oil well (active) | 100–10,000 | bbl/day | 11–1,100 L/min |
| Amazon River average | 209,000 | m³/s | 55,000,000 GPM |