Electrical design tools and calculators

Every calculator exposes its method, units, assumptions, worked example, verification boundary, and closest editable next step.

• Voltage Drop Calculator — Voltage drop is the reduction in voltage along a conductor caused by the conductor's resistance and the load current. Excessive drop causes motors to run hot, lights to dim, and sensitive equipment to malfunction. The NEC (210.19/215.2 informational notes) recommends a maximum 3% drop on a branch circuit and 5% total from the service entrance to the final outlet. BS 7671 (IEC-derived UK standard) specifies 3% for lighting circuits and 5% for other circuits.
• Wire Size Calculator — Wire size must satisfy two criteria: ampacity (current-carrying capacity) and voltage drop. First, find the minimum AWG from NEC Table 310.16 that meets the breaker or load current at the appropriate temperature rating (60 °C, 75 °C, or 90 °C). Then check that voltage drop over the run length stays within 3% (NEC recommendation). The calculator evaluates both and reports the larger required size.
• Conduit Fill Calculator — Conduit fill is the percentage of a conduit's internal cross-sectional area occupied by conductors. The NEC limits fill to prevent heat buildup (too many current-carrying conductors raise temperature and reduce ampacity) and to ensure conductors can be pulled in and out without damage. NEC Chapter 9, Table 1 sets limits: 53% for one conductor, 31% for two conductors, and 40% for three or more.
• Breaker Size Calculator — The standard rule is: breaker rating ≥ 125% of the continuous load + 100% of the non-continuous load (NEC 210.20(A)). For a purely continuous load (operating for 3 hours or more), multiply the load current by 1.25 and round up to the next standard breaker size (15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100 A, etc.).
• Electrical Load Calculator — An electrical load calculation totals the maximum expected demand (in watts or volt-amps) of all circuits in a panel or service entrance. It determines the minimum service size (e.g. 100 A, 200 A) and ensures the panel is not overloaded. NEC Article 220 provides the standard method for dwelling-unit load calculations.
• Ohm’s Law Calculator — Ohm’s law describes the relationship between voltage, current, and resistance: V = I × R. The related power identities are P = V × I, P = I²R, and P = V²/R.
• Voltage Divider Calculator — For two series resistors, Vout = Vin × R2/(R1 + R2), where R2 is the lower resistor connected to the reference node.
• LED Resistor Calculator — Subtract the combined LED forward voltage from the supply voltage and divide by desired current: R = (Vs − nVf)/I. Current must be entered in amperes in the equation.
• Transformer Calculator — For an ideal transformer, Vp/Vs = Np/Ns. The voltage ratio therefore gives the winding-turn ratio.
• Motor Current Calculator — Estimated line current is Pout/(√3 × Vline × power factor × efficiency). Use watts for Pout and line-to-line volts for Vline.
• Fault Current Calculator — It is the current that could flow at a point during a short circuit, limited by utility, transformer, conductor, and other upstream impedances.