Engineer's Calculators
Working tools, not toys — every card runs in your browser, keeps a local history of your runs, and shows the formula it uses. New calculators land weekly.
By industry
Aerospace & Defense
Atmosphere, compressible flow, and flight-side math.
36 calculators →
Electrical & RF
Power, impedance, antennas, and the dB family.
55 calculators →
Mechanical
Beams, bolts, shafts, and the things that bend.
49 calculators →
Civil & Structural
Concrete, walls, and welds.
19 calculators →
Chemical & Process
Pumps, pipes, and process fundamentals.
26 calculators →
Test & Instrumentation
Bridges, amplifiers, sensors, and signal chains.
48 calculators →
Unit Conversions
Between unit systems without the 3 a.m. mistakes.
13 calculators →
All calculators
- dB ConverterConvert power between W, mW, dBm, and dBW in one shot.
- Ohm's LawEnter any two of voltage, current, and resistance — get the third plus power.
- Frequency ⇄ WavelengthWavelength for any frequency, with velocity factor for cables.
- Beam DeflectionMaximum deflection for the two textbook cases: cantilever and simply-supported.
- Standard AtmosphereISA temperature, pressure, density, and speed of sound at altitude.
- Voltage DividerVout, loading current, and dissipation for the two-resistor divider.
- Parallel ResistorsEquivalent resistance of two or three resistors in parallel.
- Wheatstone BridgeDifferential output of the four-arm bridge — the front end of half of all sensors.
- Strain Gauge OutputBridge output for a strain measurement — quarter, half, or full bridge.
- Resistor Color CodeFour-band resistor value from the band colors.
- Op-Amp GainClosed-loop gain for inverting and non-inverting configurations.
- Instrumentation Amp GainGain of the classic three-op-amp in-amp from the gain-set resistor.
- RC Low-Pass FilterCutoff frequency and time constant for the single-pole RC.
- ADC ResolutionLSB size, counts, and ideal dynamic range for an N-bit converter.
- RMS ⇄ Peak ⇄ Peak-to-PeakSine-wave conversions between RMS, peak, and peak-to-peak.
- 4–20 mA Loop ScalingConvert loop current to process value and back — with the burden check.
- Shunt ResistorDrop, dissipation, and required rating for a current-sense shunt.
- SNR ⇄ ENOBConvert between signal-to-noise ratio and effective number of bits.
- Crest FactorPeak-to-RMS ratio — the number that clips amplifiers and fools meters.
- LED Series ResistorThe resistor between your supply and the LED, plus its dissipation.
- Capacitor Energy & ChargeStored energy and charge at a given voltage.
- Battery LifeRuntime from capacity and load, with a usable-capacity derating.
- dB Voltage RatioGain in dB from two voltages — the 20·log flavor.
- VSWR / Return Loss / ΓEnter any one of VSWR, return loss, or reflection coefficient — get all of them plus mismatch loss.
- Free-Space Path LossFSPL between isotropic antennas — the first line of every link budget.
- RF Link BudgetReceived power and margin from TX power, gains, distance, and losses.
- Thermal Noise FloorkTB noise power for a bandwidth — the −174 dBm/Hz line.
- Noise Figure ⇄ Noise TemperatureConvert between NF in dB and equivalent noise temperature in kelvin.
- Cascade Noise FigureTwo-stage Friis cascade — why the LNA wins.
- Reactance (XL / XC)Inductive or capacitive reactance at frequency.
- LC Resonant FrequencyResonance of an LC pair — the Thomson formula.
- Q Factor ⇄ BandwidthLoaded Q from bandwidth, or bandwidth from Q, at a center frequency.
- Skin DepthHow deep current actually flows in a conductor at frequency.
- PCB Trace WidthIPC-2221 trace width for a current and temperature rise.
- Microstrip ImpedanceZ₀ and effective εr for a surface trace over a ground plane (Hammerstad).
- Pi AttenuatorResistor values for a Pi pad of given attenuation and impedance.
- T AttenuatorResistor values for a T pad of given attenuation and impedance.
- dBm ⇄ dBµV (50 Ω)Convert between the RF power and EMC voltage dialects.
- Frequency ⇄ Periodf to T and back, with the angular frequency thrown in.
- Dipole / Whip LengthCut lengths for a half-wave dipole and quarter-wave whip.
- Coax Loss & Power OutTotal cable loss from the per-100-ft spec, and what actually reaches the antenna.
- Doppler ShiftFrequency shift for a moving target — one-way or radar (two-way).
- Radio / Radar HorizonLine-of-sight distance from antenna heights, with standard refraction.
- Gain from BeamwidthsApproximate directive gain from the two −3 dB beamwidths.
- RF Power DensityFar-field power density from EIRP and distance — the exposure math.
- Transformer Turns RatioVoltage, current, and impedance transformation from the turns ratio.
- RC Charge TimeTime for a capacitor to reach a target percentage of the supply.
- Inductor EnergyStored energy in a current-carrying inductance.
- Bolt Torque from PreloadTightening torque for a target preload — the K-factor shortcut everyone actually uses.
- Shaft Power ⇄ TorqueP = Tω — convert between power, torque, and rotational speed.
- Gear RatioRatio, output speed, and output torque from tooth counts.
- Coil Spring RateRate of a round-wire helical compression/extension spring, plus spring index and Wahl factor.
- Belt & Pulley SpeedDriven speed, ratio, and belt velocity from pulley diameters.
- Linear Thermal ExpansionΔL = αLΔT for common structural materials.
- Axial Stress & Strainσ = F/A and ε = σ/E, with an optional yield-strength safety check.
- Shaft Torsion (Solid Round)Max shear stress τ = Tr/J for a solid circular shaft, plus optional twist angle.
- Euler Column BucklingCritical buckling load Pcr = π²EI/(KL)² with standard end conditions.
- Bearing L10 LifeBasic rating life in million revolutions and hours — ball or roller exponent.
- Flywheel Kinetic EnergyStored rotational energy E = ½Iω² from inertia and speed.
- Hydraulic Cylinder ForceExtend and retract force from pressure, bore, and rod diameter.
- Lever Mechanical AdvantageMoment balance about the fulcrum — ideal MA and load force.
- Kinetic EnergyKE = ½mv² — the energy of anything moving in a straight line.
- Gravitational Potential EnergyPE = mgh — energy banked by height.
- Projectile Range (No Drag)Range, max height, and flight time on flat ground — vacuum ballistics.
- Friction ForceMaximum static friction μN, with an optional slides-or-holds check.
- Mass Moment of Inertia (Shapes)Rotational inertia for the four shapes that cover most machine parts.
- Rectangular Section ModulusS = bh²/6 and I = bh³/12, with optional bending stress from a moment.
- Thin-Wall Pressure Vessel StressHoop and longitudinal stress σ = Pr/t, with the r/t > 10 validity gate.
- Plate Clutch Torque (Uniform Wear)Transmissible torque T = µ·F·n·R_mean for disc clutches and brakes.
- Fillet Weld Throat StressShear on the throat, a = 0.707z — the plane where fillet welds actually fail.
- Shaft Critical Speed (Deflection Method)First critical speed from static deflection — the Rayleigh one-liner.
- Natural Frequency (Spring–Mass)f = (1/2π)√(k/m) — the fundamental note of any stiffness and mass.
- Pendulum PeriodT = 2π√(L/g) — small-swing period of a simple pendulum.
- Speed of Sound in MaterialsLongitudinal bar velocity c = √(E/ρ) for common engineering solids.
- Isentropic Flow RatiosT/T₀, P/P₀, ρ/ρ₀, and A/A* from Mach number — the compressible-flow table, minus the table.
- Normal Shock RelationsJump conditions across a normal shock: M₂ and the pressure, density, temperature, and total-pressure ratios.
- Oblique Shock (θ-β-M)Weak-shock angle β and downstream conditions for a wedge at supersonic speed — with detached-shock detection.
- Mach Number from Airspeed & AltitudeTrue airspeed plus ISA altitude → Mach number and the local speed of sound.
- Dynamic Pressure (q)q = ½ρV² from velocity plus either an ISA altitude or a direct density.
- Reynolds NumberRe = ρVL/µ with one-click air or water properties, or your own fluid.
- Pipe Pressure Drop (Darcy-Weisbach)Friction loss in a round pipe — Swamee-Jain friction factor, automatic laminar branch.
- Pipe Flow VelocityMean velocity in a round pipe from volumetric flow and diameter.
- Bernoulli Pressure ChangeDownstream pressure from an upstream state, two velocities, and an elevation change.
- Orifice FlowFlow through a sharp-edged orifice from a pressure differential — Q = C_d·A·√(2ΔP/ρ).
- Manning Open-Channel FlowDischarge in a rectangular channel from geometry, slope, and roughness n.
- Pump Hydraulic & Shaft PowerWater power from flow and head, and the shaft power once efficiency takes its cut.
- NPSH AvailableNet positive suction head at the pump inlet — the cavitation margin.
- Airflow Units (CFM ⇄ m³/h ⇄ L/s)The three dialects of volumetric airflow, converted exactly.
- SCFM ⇄ ACFMStandard-to-actual airflow via the ideal-gas temperature and pressure correction.
- Drag ForceF = ½ρV²·C_d·A — aerodynamic drag and the power it costs.
- Lift ForceL = ½ρV²·C_L·S — lift from speed, wing area, and lift coefficient.
- Terminal VelocitySteady fall speed where drag balances weight: √(2mg / ρ·C_d·A).
- Tsiolkovsky Rocket EquationΔv from specific impulse and mass ratio — the tyranny, quantified.
- Circular Orbit Velocity & PeriodSpeed and period of a circular Earth orbit from altitude.
- Escape Velocity√(2µ/r) for Earth, Moon, or Mars — from the surface or from altitude.
- Hohmann TransferTwo-burn transfer between circular Earth orbits: Δv₁, Δv₂, total, and time of flight.
- Specific ImpulseI_sp and effective exhaust velocity from thrust and propellant mass flow.
- Water Hammer (Joukowsky)Pressure surge from a sudden velocity change: ΔP = ρ·a·Δv.
- Pressure ConverterPa, kPa, bar, psi, atm, mmHg, inH₂O, and Torr — one value, every dialect.
- Volumetric Flow ConverterL/s, L/min, m³/h, US GPM, and CFM — pump curves to duct specs.
- Torque ConverterN·m, lbf·ft, lbf·in, kgf·m, and ozf·in — wrench specs in every dialect.
- Energy ConverterJ, kJ, Wh, kWh, BTU, cal, ft·lbf — plus the eV for the physicists.
- Power ConverterW, kW, both horsepowers, BTU/h, and tons of refrigeration.
- Temperature Converter°C, °F, K, and °R — the one conversion with offsets, done right.
- Length Convertermm to nautical miles, with the PCB designer's mil in between.
- Mass & Force Converterkg, lb, oz, slug — and their weights in N, kgf, lbf at standard gravity.
- Area & Volume Converterm², ft², in² and L, gal(US), ft³, m³ — enter either or both.
- Angle ConverterDegrees, radians, gradians, arcminutes, mrad — and the NATO mil.
- Speed Converterm/s, km/h, mph, knots, ft/s — with the sea-level Mach number thrown in.
- Concrete Slab VolumeSlab volume from length, width, and thickness — plus bag counts and a waste allowance.
- Concrete Column VolumeVolume for round or square columns, any count — with bag equivalents.
- Concrete Block WallCMU count and mortar bags for a wall — standard 8×16 block.
- Rebar WeightTotal weight for a run of US bar sizes #3–#8.
- Aggregate TonnageTonnes of gravel, sand, or crushed stone from area and depth.
- Rankine Earth PressureActive earth pressure coefficient and resultant force on a retaining wall.
- Horizontal Tank VolumePartial-fill volume of a horizontal cylindrical tank from the dip level.
- Vertical Tank VolumeFill volume of a vertical cylindrical tank from the level.
- Ideal Gas Law (PV = nRT)Leave any one of P, V, n, T blank — the card solves for it.
- Gas DensityDensity of a gas from pressure and temperature — ρ = PM/RT.
- Log-Mean Temperature DifferenceLMTD for counterflow or parallel-flow heat exchangers from the four terminal temperatures.
- Heat Exchanger DutyQ = ṁ·cp·ΔT for one stream — the first number of every exchanger problem.
- Heat Conduction (Fourier)Steady heat flow through a flat layer — Q = k·A·ΔT/L.
- Dilution (C₁V₁ = C₂V₂)Leave any one of the four blank — stock, dose, or final volume solved.
- Pump Head ⇄ PressureConvert a pressure to metres of head for a fluid, plus static lift.
- Arrhenius Rate RatioHow much faster a reaction runs at a new temperature, from the activation energy.
- Half-Life DecayFraction remaining after any elapsed time, from the half-life.
- Dew Point & Absolute HumidityDew point from temperature and relative humidity — Magnus formula, plus g/m³ of water.
- L-Network Impedance MatchTwo-component L-match between resistive source and load — Q, L, and C at your frequency.
- 555 Timer — AstableR1, R2, C → frequency, duty cycle, and high/low times for the classic astable hookup.
- 555 Timer — MonostableOne-shot pulse width from R and C: t = 1.1·R·C.
- Zener Shunt RegulatorSeries resistor window and worst-case zener dissipation for a simple shunt regulator.
- Wire Gauge (AWG) PropertiesPick an AWG size — diameter, area, resistance, and rule-of-thumb ampacity for copper.
- Wire Voltage DropRound-trip drop over a copper pair: AWG size, one-way length, and load current.
- Power Sum in dBmAdd two incoherent powers expressed in dBm — the right way.
- Fresnel Zone ClearanceFirst-zone radius at mid-path and the 60% clearance a microwave link actually needs.
- ERP ⇄ EIRPRadiated power against the dipole or isotropic reference — the 2.15 dB everyone flips.
- Coax Impedance from DimensionsZ₀ of a coaxial line from shield ID, center-conductor OD, and the dielectric.
- Series RLC Impedance|Z| and phase of a series R-L-C at frequency, plus where it resonates.
- Battery Pack ConfigurationSeries × parallel cells → pack voltage, capacity, and watt-hours.
- Hold-Up Capacitor SizingBulk capacitance to ride through a dropout: C = 2·P·t / (V₁² − V₂²).
- Nearest E-Series ValueSnap a target resistance to the nearest E12 / E24 / E96 standard value.
- LED Array / String DesignerSupply, Vf, and current → LEDs per string, string count, and the ballast resistor.
- RC Snubber (Ring Killer)Size R and C from the measured ringing frequency and estimated parasitic capacitance.
- Inrush Limiter (NTC) SizingCold resistance to cap the surge into a capacitor bank, and the joules the NTC must swallow.