Flow Rate Calculator
Calculate flow rate instantly in your browser — the published formula, worked locally with no data sent anywhere.
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What this tool does
Calculate flow rate instantly in your browser — the published formula, worked locally with no data sent anywhere. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
How to use the Flow Rate Calculator
- Enter or select cross-section.
- Enter or select cross-sectional area in sqft.
- Enter or select pipe inside diameter in in.
- Enter or select flow velocity (ft/s).
- Read the calculated result; change any measurement to compare alternatives.
Formula
volumetric flow rate Q = A × v (area times mean velocity). A round pipe's area is π × (d/2)². 1 cu ft/s = 448.831 US gal/min.
- mode
- Cross-section
- area
- Cross-sectional area (sqft, before metric conversion)
- diameter
- Pipe inside diameter (in, before metric conversion)
- velocity
- Flow velocity (ft/s)
Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
Worked example
For flow rate calculator, the following measurements illustrate the exact method: Cross-section: area; Cross-sectional area: 0.5; Pipe inside diameter: 4; Flow velocity (ft/s): 10.
Inputs
- Cross-sectionKnown area
- Cross-sectional area0.5 sq ft
- Pipe inside diameter4 in
- Flow velocity (ft/s)10
Result
- Flow rate (cu ft/s)5
- Flow rate (US gal/min)2,244.16
- Flow rate (L/s)141.58
- Flow rate (m³/h)509.7
- Cross-sectional area (sq ft)0.5
Results explained
- Flow rate (cu ft/s)
- Flow rate (cu ft/s) from the formula above. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
- Flow rate (US gal/min)
- Flow rate (US gal/min) from the formula above. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
- Flow rate (L/s)
- Flow rate (L/s) from the formula above. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
- Flow rate (m³/h)
- Flow rate (m³/h) from the formula above. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
- Cross-sectional area (sq ft)
- Cross-sectional area (sq ft) from the formula above. Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
Frequently asked questions
volumetric flow rate Q = A × v (area times mean velocity). A round pipe's area is π × (d/2)². 1 cu ft/s = 448.831 US gal/min.
Uses the mean velocity across the whole cross-section. Real pipe flow is fastest at the centre and near zero at the walls, so a centre-line probe reading overstates Q unless corrected.
Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.
It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.
Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.