Field Pocket Guide

Flow Calculator

Calculate, convert and compare flow: differential-pressure meters with their own ISO equations, explicit gas reference states so SCFM and ACFM never get mixed, signal and pulse conversions, and live flow curves. It runs entirely in your browser and ships with its own regression checks. Demonstration inputs are not equipment calibration data.

Standard flow requires a stated reference. SCFM is not interchangeable with ACFM. Demonstration inputs are not equipment calibration data.

How to read this form:Required enter to get a resultCompensation pressure, temperature & reference move the resultOptional refine or document

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Guided setup

Talk to it

Describe your meter in plain words. The wizard collects the numbers, runs the exact engine, and shows the curve and tables right here in the chat. Ask it for a spec sheet any time.

The wizard only asks questions and runs the calculator. Every number comes from the deterministic engine, not the AI.

Calculation

Required

Start here: the meter type, the fluid, and what to solve for. Then enter the primary measurement below.

Meter type / calculation mode

Fluid phase

Solve for

Flow rate

The selected flow unit is also used for the graph.

Convert to / graph unit

Differential pressure ΔP

Measured DP, not static line pressure, pressure loss, or a square-rooted signal.

DP limit · separate from measured DPOptional

Your documented limit. It does not set transmitter span, chart range, or a safety rating.

Geometry & coefficients

Required

Primary-element bore and discharge coefficient. These set the meter’s size and shape.

Actual pipe internal diameter D

Bore at operating temperature, not nominal pipe size.

Effective beta ratio β

Circular bore: d/D. Cone/wedge: √(open area / pipe area).

Geometry entry

Bore / opening dimension

Uses the diameter unit selected above.

Discharge coefficient source

Discharge coefficient C

Orifice pressure taps

Dimensionless flow coefficient K

Demonstration only. Must match Q = K·Y·A·√(2ΔP/ρ).

Mean / local velocity factor

Single-point pitot only. Obtain from a traverse or validated profile.

Gas expansion method

Gas expansion factor Y

Separate from compressibility Z. Y = 1 neglects local expansion.

Instrument inputs

Required

The measured value and calibration for this meter type.

Cross-section

Duct width

Duct height

Cross-sectional area

m²

Mean velocity

m/s

Pulse frequency

Pulse K

pulses/unit

Unit counted by pulse K

Volume represented by each pulse

Signal represents

Signal value

signal units

Signal range low

Signal range high

Flow range low

Flow range high

Flow range units

Calibration actual flow

Calibration flow units

Calibration differential

Uses the selected DP unit.

Calibration fluid density

kg/m³

Calibration expansion Y

Operating expansion Y

Flowing gas conditions

Compensation

Pressure, temperature and compressibility set the flowing density and compensate the flow — the biggest lever on the result. Get these right before trusting the number.

Upstream / line static pressure

Flowing temperature

All temperature ratios use absolute kelvin internally.

Local atmospheric pressure

101.325 kPa is a reference atmosphere, not a local barometer reading.

Dry-gas molar mass M

kg/kmol

Dry mixture excluding separately entered water vapor. Air example: 28.96546.

Flowing gas-density method

Flowing compressibility Z

Not the DP expansion factor. Z = 1 explicitly assumes ideal-gas behavior.

Flowing gas density ρ₁

Calculated from the mixture molar mass and flowing state.

Liquid density at flowing conditions

No automatic water-property or thermal-volume-correction model is applied.

Isentropic exponent κ

Use the fluid’s exponent at line conditions. Cp/Cv is an ideal-gas approximation.

Gas dynamic viscosity μ

Used for ReD. Example only; no temperature correlation.

Liquid dynamic viscosity μ

Enter the actual fluid viscosity for Reynolds checks.

Water vapor and reporting basis

Water-vapor mole fraction

mol %

Not % relative humidity. 2 here means yH₂O = 0.02.

Reference volume represents

Both standard and normal outputs use this choice. Mass outputs always describe the total flowing stream.

Single-phase gas at the meter is assumed. No saturation or condensation prediction is included; do not use this as a wet-steam or two-phase solver.

Reference conditions for SCFM

Compensation

Defines what “standard” means. Changes every S-prefixed number (SCFM and the rest); it does not change actual flow.

Reference-state preset

A preset sets P and T only; it does not calculate Z. The ISO 13443 preset also selects dry reporting.

Reference temperature Ts

Reference pressure Ps · absolute

Zs at the selected reference

For the selected dry/total gas composition.

Zn at the fixed normal reference

0 °C and 101.325 kPa absolute. Normal output is independent of the SCFM preset.

Current report basis

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Calculation / calibration / property source noteOptional

Included with saved reports. No device, serial number or vendor is assumed.

INITIALIZING

Calculated flow

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Actual flow

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ACFM

Normal flow

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Nm³/h

Total mass

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kg/h

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Flow curves

Curve

X start

X end

Overlay actual-volume flow on the same volume/time scale

Move across the curve to inspect values.

Curve data & excluded ranges

Input	Flow	Status

Calculated state & meter diagnostics

DP is not permanent pressure loss. Numerical checks do not certify installation or measurement uncertainty.

Show the calculation · equations & substitutions

All flow units · actual / standard / normal / mass

Unit and basis	Value

Assumptions & applicability

An engineering calculation tool, not a certified sizing service or custody-transfer package. Verify inputs before changing live equipment.

Equations, standards & implementation coverage

Coverage is explicit, not a blanket compliance claim. Each DP type uses its own equation or a clearly identified entered-coefficient model. Geometry, taps, installation, uncertainty, real-gas properties and equipment ratings remain the user's responsibility. This is not a control-valve Cv/Kv, choked-flow, wet-steam, multiphase, open-channel or pipe-network solver.

S1 · Classical Venturi

ISO 5167-4:2022 numerical coefficient profiles and expansibility; checks D, β, Re and pressure ratio. Physical geometry, roughness and straight lengths are not audited.

ISO 5167-4:2022

S2 · Orifice plate

Reader–Harris/Gallagher (1998) coefficient with corner, flange or D–D/2 taps. Equation transcription and numerical bounds verified against ISO 5167-2:2003 §§5.3.1–5.3.2; the current standard is linked separately. No extrapolation below its Re limit.

ISO equation source (2003) · Current ISO 5167-2:2022 scope

S3 · Nozzles

ISA 1932, long-radius and Venturi-nozzle correlations transcribed from ISO 5167-3:2003; ISA 1932 also cross-checked in the 2020 preview. Throat-tapped mode requires entered C and Y. “ISA 1932” names a geometry, not modern ISA control-valve sizing.

ISO nozzle equation source · ISO 5167-3:2022 scope

S4 · Cone, wedge & custom elements

Entered C/Y or K/Y only; no automatic ISO 5167-5/-6 coefficient claim. β² is the open-area fraction for cone and wedge. A coefficient must match the equation displayed, not just the letter K or C.

ISO 5167-6:2022 scope

S5 · Pitot / averaging pitot

Dimensionless coefficient in Qa = K·Y·A·√(2ΔP/ρ). Single-point mode adds an entered mean/local velocity factor. No manufacturer's proprietary coefficient curve is inferred.

Primary-element theory reference

S6 · Flow units & reference states

SI conversion core; absolute P and T; independent flowing and reference Z. Normal units are fixed at 0 °C / 101.325 kPa abs. Standard units use the selected, printed reference state.

NIST gas-flow reference warning · NIST unit factors

S7 · Signal & continuity models

Q = v̄A; frequency divided by pulse K; affine analog scaling or one square-root extraction. These are transparent algebraic conversions, not a new calibration for magnetic, ultrasonic, vortex, turbine, thermal or Coriolis instruments.

S8 · Curves & limitations

Each plotted point is recalculated. No-data regions are not bridged. Pressure/temperature sweeps hold entered composition, Z, viscosity, κ and calibration constants fixed; they are sensitivity curves, not an EOS or equipment performance prediction.

S9 · Source review

13 October 2026. No copied standards or proprietary calibration databases are bundled. Linked standards remain the authority for their applicable edition. Run the embedded software checks; passing arithmetic tests does not certify a physical installation.

Software regression checks