Engineering & Electrical calculators

Voltage drop, wire gauge, gear ratios, beam loads, and HVAC BTU sizing

555 Timer CalculatorCompute astable 555 frequency, period, duty cycle, and pulse times from R1, R2, and CAntenna Gain CalculatorEstimate antenna gain in dBi from E-plane and H-plane half-power beamwidths using the beam-area approximation - for dish, horn, and Yagi antenna design.Beam Load CalculatorCalculate support reactions, maximum shear force, and bending moment for a simply supported beam with point or distributed loads. Free.Bolt Torque CalculatorCalculate bolt tightening torque from nominal diameter, target preload, and nut factor K for accurate fastener assembly. Free, instant.Capacitor Network CalculatorCalculate the total equivalent capacitance of capacitors connected in series or in parallelCurrent Mirror Output CalculatorCalculate the ideal output current of a current mirror from the reference current and the output-to-reference device size ratiodBm to Watt ConverterConvert between dBm, milliwatts, and watts for RF power level calculations in wireless, antenna, and signal engineering. Free, instant.Dipole Antenna Length CalculatorCalculate the total and per-leg length of a half-wave dipole antenna from frequency using the practical 468 end-effect constantElectrical Wire Gauge CalculatorFind the correct wire gauge based on amperage, distance, and voltage drop limits per NEC codeEuler Column Buckling CalculatorCalculate the critical Euler buckling load of a slender column from its modulus, moment of inertia, length, and end conditionsFactor of Safety CalculatorCalculate the factor of safety from a material strength and the applied working stress, with a plain assessment of the marginFree Space Path Loss CalculatorCalculate free space path loss in decibels from link distance and frequency using the Friis equationGear Ratio CalculatorCalculate gear ratio, output shaft RPM, and torque multiplication or reduction for any gear pair or multi-stage gear train. Free.Hooke's Law Spring CalculatorCalculate the spring force and stored elastic potential energy from the spring constant and displacement using Hooke's lawHoop Stress CalculatorCalculate the hoop and longitudinal stresses in a thin-walled pressure vessel from internal pressure, inner radius, and wall thicknessHVAC Load / BTU CalculatorEstimate heating and cooling BTU requirements based on room volume, climate, and insulationInductor Energy CalculatorCalculate the energy stored in an inductor's magnetic field in joules and millijoules from its inductance and currentkVA, kW & Power Factor CalculatorConvert between apparent power, real power, reactive power, power factor, and currentLED Series Resistor CalculatorFind the current-limiting resistor for an LED from supply voltage, forward voltage, and currentMicrostrip Impedance CalculatorCalculate the characteristic impedance and effective permittivity of a microstrip trace from width, substrate height, and dielectric constantMOSFET Conduction Loss CalculatorCalculate the conduction power loss in a MOSFET from drain current, Rds(on), and duty cycleMotor Full-Load Current CalculatorEstimate the full-load current of a single-phase or three-phase motor from power, voltage, power factor, and efficiencyOhm's Law CalculatorApply Ohm's Law (V = IR) to calculate voltage, current, resistance, or power - with unit conversions for electronics and electrical engineering problems.Op-Amp Gain CalculatorCalculate inverting and non-inverting op-amp voltage gain from feedback and input resistors, with gain in decibels and an optional output voltageParallel Plate Capacitance CalculatorCalculate the capacitance of a parallel plate capacitor from plate area, separation, and dielectric constantParallel Resistance CalculatorCalculate the total equivalent resistance of two to four resistors in parallel - always less than the smallest individual resistor in the network.PCB Trace Width CalculatorSize minimum PCB trace width from target current and allowable temperature rise using the IPC-2221 standard external and internal tables. Free.Pulley & Belt CalculatorCalculate driven shaft RPM, belt length, and belt speed for a two-pulley V-belt or flat-belt drive from pulley diameters and center distance. Free.Pump Horsepower CalculatorCalculate hydraulic and brake horsepower from flow rate, head, and pump efficiencyPump Hydraulic Power CalculatorCalculate the hydraulic and shaft power of a pump in kilowatts from flow rate, head, efficiency, and fluid densityRC Filter Cutoff Frequency CalculatorCalculate the minus three decibel cutoff frequency of an RC low-pass or high-pass filter from resistance and capacitanceReactance CalculatorCalculate capacitive and inductive reactance at any frequency, and find the LC resonant frequency for filter and circuit design. Free.Resistor Color Code CalculatorDecode 4 or 5 band resistor color codes to find the resistance value and tolerance, or look up the color bands for a given resistance. Free.Resistor Series & Parallel CalculatorSeries and parallel resistance calculator: find equivalent resistance instantly for circuit design with up to six resistors in any mixRL Time Constant CalculatorCalculate the time constant and settling time of an RL circuit from inductance and resistanceSkin Depth CalculatorCalculate the skin depth of a conductor in meters and micrometers from frequency, resistivity, and relative permeabilitySolenoid Inductance CalculatorCalculate the inductance of a solenoid coil from turns, core area, length, and relative permeabilityTap Drill Size CalculatorTap drill size chart for UNC, UNF, and metric threads. Set thread engagement and get the exact drill diameter for any tap sizeThermal Conduction CalculatorCalculate the steady-state heat transfer rate through a wall using Fourier's law from conductivity, area, temperature difference, and thicknessThree-Phase Power CalculatorCalculate three-phase real, apparent, and reactive power, current, or power factorTransformer Sizing CalculatorSize a transformer in kVA and find primary/secondary full-load amps for 1- or 3-phase loadsTransformer Turns Ratio CalculatorCalculate a transformer's turns ratio and secondary voltage from the primary and secondary turn counts and the primary voltageTransmission Line Length CalculatorCalculate quarter-wave and half-wave transmission line lengths from frequency and cable velocity factorVoltage Divider CalculatorFind output voltage, current, and power for a two-resistor voltage divider networkVoltage Drop CalculatorCalculate voltage drop in a wire run by AWG size, distance, current, and materialVSWR & Return Loss CalculatorCalculate VSWR, return loss, and reflection coefficient from forward and reflected power on a transmission lineWheatstone Bridge CalculatorCalculate the unknown resistance in a balanced Wheatstone bridge from the three known resistor valuesYoung's Modulus CalculatorCalculate stress, strain, and Young modulus from applied force, cross-sectional area, original length, and elongation

About Engineering & Electrical Calculators

Engineering and electrical calculators are the field-reference tools that electricians, mechanical engineers, and serious DIYers reach for during design, install, and inspection. The collection focuses on the everyday calculations that drive real decisions: what wire gauge to pull, how much voltage you'll lose over a long run, how a beam will deflect under load, and what gear ratio a drivetrain actually delivers. Every electrical tool follows National Electrical Code (NEC) NFPA 70 conventions: copper and aluminum resistivity at 75 °C ampacity ratings, 3% maximum branch-circuit voltage drop and 5% combined feeder + branch as the recommended limit per NEC 210.19(A) and 215.2(A) Informational Notes, and standard AWG sizes from 18 AWG up through 4/0 and into kcmil for service entrances.

The voltage drop and wire gauge calculators are the two most-used. Voltage drop uses Vd = (2 × K × I × L) / CM for single-phase and (1.732 × K × I × L) / CM for three-phase, with K = 12.9 ohm-circular-mil/foot for copper at 75 °C and 21.2 for aluminum, matching the values in NEC Chapter 9 Table 8. The wire gauge calculator works the inverse problem: given a current, distance, and acceptable drop, what AWG do you need? Both tools warn when ampacity (NEC Table 310.16) becomes the binding constraint rather than voltage drop, which is the mistake that most homeowner-grade calculators make.

Mechanical tools are equally rigorous. The beam load calculator handles simply-supported beams under point and uniformly distributed loads, returning reactions, maximum shear, maximum moment, and the location of zero shear. The gear ratio calculator computes ratio, output RPM, and torque multiplication for any single pair, with a compound-gear mode for trains of two or three meshes. HVAC load and BTU calculations use the standard rule-of-thumb factors (20-60 BTU/hr per cubic foot depending on insulation and climate zone) for quick sizing, with a note that ACCA Manual J is the right tool for permitting work.

Most users land here mid-project: running new circuits in a workshop, sizing a generator, designing a custom CNC drivetrain, or checking whether a contractor's spec is reasonable. The calculators show every intermediate value (circular mils, K-factor, derating) so the work is auditable for an electrical inspector or a stress analyst. Material properties come from MIL-HDBK-5J, the AISC Steel Construction Manual, and the NEC for electrical, so the constants reconcile to the references your AHJ will recognize.

When to Use a Engineering & Electrical Calculator

  • Sizing branch circuits or feeders to meet NEC 3% / 5% voltage drop targets
  • Choosing AWG wire gauge for a specific amperage and run length on copper or aluminum
  • Calculating reactions, shear, and bending moment for a simply supported beam
  • Designing a gear train and predicting output RPM and torque from input power
  • Estimating HVAC load in BTU/hr for a quick sizing check before formal Manual J
  • Verifying that an electrician or mechanical engineer's spec is in a reasonable range

Frequently Asked Questions

What voltage drop percentage does NEC actually require?

NEC doesn't mandate a maximum voltage drop in the enforceable code itself. The recommendations are in Informational Notes to 210.19(A)(1) for branch circuits and 215.2(A)(1) for feeders. The widely accepted targets are 3% on the branch circuit, 2% on the feeder, and 5% combined. Some local AHJs adopt these as enforceable; check before you submit a design.

Can I use copper voltage drop numbers for aluminum wire?

No. Aluminum has roughly 1.6× the resistivity of copper, so for the same current and distance you need to go up about two AWG sizes. Our calculators have an explicit conductor-material toggle, so always select the actual material being installed, not the one the formula defaulted to.

What's the difference between ampacity and voltage drop sizing?

Ampacity (NEC Table 310.16) is about heat: what current the conductor can carry without exceeding its insulation rating. Voltage drop is about delivered voltage at the load. On short runs ampacity governs; on long runs voltage drop usually requires a larger conductor than ampacity alone would. Always size to the more demanding of the two.

Are the beam calculations good for permit-stamped drawings?

They're accurate for simply-supported beams under standard loadings, but a stamped drawing requires a licensed PE in your jurisdiction to seal the analysis. Use the calculator for preliminary sizing, sanity-checking a contractor, or coursework, not as the final basis for construction.

Is BTU sizing from this calculator enough for an HVAC permit?

No. Most jurisdictions require ACCA Manual J for residential and Manual N for commercial as the basis for permit-grade load calculations, because they account for solar gain, infiltration, internal loads, and duct losses individually. Our HVAC tool is a quick rule-of-thumb sizing for budgeting and feasibility checks.

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