Instrumentation calculators that get the numbers right

Free online calculators for process and instrumentation engineers: 4–20 mA scaling, RTD & thermocouple conversion, pressure, flow, level, control valves and calibration — no signup, no fluff.

4 mA 0% 8 mA 25% 12 mA 50% 16 mA 75% 20 mA 100%

    Calculators

    Signal & Loop

    4-20 mA to Process Variable (PV) Calculator

    Convert loop current to process value, percentage and back — with any range.
    Signal & Loop

    mA to Percentage Converter

    Instant 4-20 mA ↔ 0-100 % conversion.
    Signal & Loop

    Current Loop Voltage Drop Calculator

    Will your transmitter power up? Check supply voltage vs loop resistance.
    Signal & Loop

    5-Point Calibration Table Generator

    Generate 0-25-50-75-100 % test points in mA and engineering units.
    Signal & Loop

    Square Root Extraction Calculator (DP ↔ Flow)

    Convert DP signal to flow percentage and mA — the √ law done right.
    Temperature

    PT100 / PT1000 Resistance ↔ Temperature Calculator

    Callendar–Van Dusen conversion both ways, Class A/B tolerance included.
    Temperature

    Temperature Unit Converter (°C ↔ °F ↔ K ↔ °R)

    Celsius, Fahrenheit, Kelvin and Rankine in one live grid.
    Temperature

    Thermocouple mV ↔ Temperature Calculator

    Types K, J, T, E, N, R, S, B with cold junction compensation.
    Pressure

    Pressure Unit Converter — psig, barg, kPa, kg/cm², mmWC

    bar, psi, kPa, kg/cm², mmH2O, inH2O, mmHg, Torr, atm — all at once.
    Pressure

    Hydrostatic Pressure / Liquid Head Calculator

    Pressure from liquid height and density (and back).
    Pressure

    Gauge to Absolute Pressure Converter — barg ↔ bara, psig ↔ psia

    psig to psia, barg to bara — with altitude-corrected atmospheric pressure.
    Level & Tank

    DP Transmitter Level Calculation — Open Tank

    Range, LRV/URV and mA output for open-tank DP level.
    Level & Tank

    Vertical Cylindrical Tank Volume Calculator — Litres from Level

    Volume at any level, total capacity, litres and m³.
    Level & Tank

    Horizontal Cylindrical Tank Volume Calculator with Dip Chart

    Partial-fill volume from liquid depth — the circular segment done right.
    Flow

    Flow Unit Converter

    m³/h, L/min, GPM, BBL/d, kg/h, Nm³/h, SCFM in one place.
    Flow

    Pipe Velocity Calculator

    Velocity from flow rate and pipe ID — with recommended velocity limits.
    Flow

    Mass ↔ Volumetric Flow Converter

    kg/h ↔ m³/h with density — edit any of the three.
    Control Valves

    Control Valve Cv Sizing — Liquid

    Required Cv from flow, ΔP and specific gravity.
    Control Valves

    Cv ↔ Kv Converter

    Valve flow coefficients: US Cv, metric Kv and SI Av.
    Electrical

    Cable Voltage Drop Calculator — Single & Three Phase, Copper & Aluminium

    Voltage drop and % drop for copper/aluminium, 1-φ and 3-φ.
    Electrical

    Ohm's Law Calculator (V, I, R, P)

    Enter any two of voltage, current, resistance, power — get the rest.
    Electrical

    Three-Phase Power Calculator (kW ↔ kVA ↔ Amps)

    kW, kVA, kVAR and line current from voltage and power factor.
    Process & General

    PID Tuning Calculator (Ziegler–Nichols & Cohen–Coon)

    P, PI, PID settings from process test data.
    Calibration

    Instrument Error Converter — % Span ↔ % Reading

    Convert accuracy specs between % of span, % of reading and absolute units.
    Calibration

    TUR Calculator (Test Uncertainty Ratio)

    Is your calibrator good enough? Tolerance ÷ standard uncertainty with verdict.
    Analyzers

    Gas Concentration Converter (ppm ↔ mg/m³ ↔ %LEL)

    Convert gas concentration units with molecular weight.
    Level & Tank

    DP Transmitter Level Calculation — Closed Tank

    LRV/URV with dry leg or wet leg — zero elevation done right.
    Flow

    Actual ↔ Standard Gas Flow Converter (Am³/h ↔ Nm³/h, ACFM ↔ SCFM)

    Gas-law correction between operating and reference conditions.
    Flow

    Reynolds Number Calculator — Laminar or Turbulent Flow

    Laminar or turbulent? Re from velocity, diameter, density and viscosity.
    Process & General

    Density ↔ SG ↔ °API Converter

    Petroleum gravity scales: density, specific gravity, API and Baumé.
    Control Valves

    I/P Converter Scaling (4-20 mA ↔ 3-15 psi)

    Current to pneumatic signal — mA, psi, kPa and bar in one place.
    Electrical

    Resistor Color Code Calculator (4, 5 & 6 Band)

    Bands to resistance value, tolerance and tempco.
    Electrical

    Motor Full Load Current Calculator

    FLC from kW, voltage, power factor and efficiency — 1φ and 3φ.
    Process & General

    Ideal Gas Law Calculator (PV = nRT & Gas Density)

    Gas density, molar volume and PV=nRT from pressure, temperature and MW.
    Calibration

    Hysteresis & Repeatability Calculator

    From up/down calibration readings to % of span numbers.
    Temperature

    RTD Lead Wire Resistance Error Calculator

    2-wire vs 3-wire vs 4-wire — the °C error from your cable.
    Flow

    Pipe Schedule & Dimensions Lookup (ASME B36.10M)

    NPS + schedule → OD, wall, ID, weight and internal area.
    Flow

    Orifice Plate Sizing Calculator — Bore & Beta Ratio (ISO 5167)

    Bore and beta ratio from flow and differential pressure.
    Electrical

    Cable Ampacity & Derating Calculator (IEC 60364)

    Base rating with ambient, grouping and insulation derating factors.
    Process & General

    Saturated Steam Table (Pressure ↔ Temperature)

    Tsat, enthalpy and specific volume from pressure — or the reverse.
    Control Valves

    Control Valve Cv Sizing — Gas & Steam (IEC 60534)

    Compressible sizing with expansion factor and choked-flow check.
    Level & Tank

    Tank Volume Calculator with Dished Heads (2:1 Elliptical, ASME F&D)

    Real tank volume including head geometry — vertical or horizontal.
    Process & General

    NPSH Available Calculator (Pump Cavitation Margin)

    NPSHa from suction conditions, with margin against pump NPSHr.
    Electrical

    Hazardous Area Equipment Marking Decoder (Ex, ATEX, IECEx)

    Decode Ex db IIC T4 Gb — protection, gas group, temperature class.
    Control Valves

    Control Valve Characteristic & Installed Gain Calculator

    Inherent vs installed curves from valve authority — linear, equal % or quick opening.
    Signal & Loop

    ISA Instrument Tag Number Decoder (ISA 5.1)

    Decode or build tags like FIC-101, PDT-205, LAHH-310.
    Flow

    Pipe Pressure Drop Calculator (Darcy-Weisbach & Colebrook)

    Friction loss per 100 m with the real friction factor, not a chart.
    Control Valves

    Pressure Relief Valve Sizing Calculator (API 520)

    Required orifice area for gas, steam or liquid relief.
    Calibration

    SIL & PFD Calculator (IEC 61511 Safety Loops)

    PFDavg and risk reduction factor from failure rate and proof test interval.
    Analyzers

    pH Electrode Slope & Nernst Calculator

    Electrode efficiency and offset from two-point buffer calibration.
    Analyzers

    Compressed Air Dew Point Converter (Pressure ↔ Atmospheric)

    Pressure dew point to atmospheric dew point, with ISO 8573-1 class.
    Process & General

    Vibration Severity Calculator (ISO 10816 Zones)

    Machine condition zone from velocity, plus displacement and acceleration.
    Temperature

    Thermowell Wake Frequency Calculator (ASME PTC 19.3 TW)

    Vortex shedding vs natural frequency — will the thermowell survive?
    Flow

    Flow Meter K-Factor Calculator (Pulses to Flow Rate)

    K-factor, pulse frequency, flow rate and meter factor in one place.
    Control Valves

    Control Valve Seat Leakage Class Calculator (FCI 70-2 / ANSI I-VI)

    Allowable leakage rate for Class II through VI.
    Analyzers

    Conductivity, TDS & Resistivity Converter with Temperature Compensation

    µS/cm ↔ ppm ↔ MΩ·cm, compensated to 25 °C.
    Analyzers

    Combustion Excess Air & Efficiency Calculator (from O₂)

    Excess air, lambda and stack loss from flue gas oxygen.
    Process & General

    Instrument Air Consumption & Receiver Sizing Calculator

    Total air demand and backup receiver volume for a given ride-through.

    Browse by category

    Signal & Loop

    4-20 mA scaling, loop power, calibration points and signal conversion.

    Temperature

    RTD and thermocouple conversion, tolerances and temperature units.

    Pressure

    Pressure unit conversion, hydrostatic head and DP level calculations.

    Flow

    Flow unit conversion, DP-to-flow, orifice sizing and gas flow correction.

    Level & Tank

    Tank volume, level-to-volume and level instrument calculations.

    Control Valves

    Cv / Kv sizing and control valve calculations.

    Electrical

    Cable sizing, voltage drop, power and loop wiring calculations.

    Process & General

    PID tuning, unit conversions and fluid properties.

    Calibration

    Errors, uncertainty, test points and calibration scheduling.

    Analyzers

    pH, conductivity, and gas concentration conversions.

    Why ZeroAndSpan?

    Every calculator here is written and verified by an instrumentation engineer — formulas follow the standards (IEC 60751, ISA, NAMUR) and each tool explains its math with a worked example, so you can check the result instead of trusting a black box. Zero and span: the two adjustments every instrument needs, and the two things this site promises to get right.