Free electrical engineering calculators
Every calculationshows its work.
A free library of electrical engineering calculators for practicing engineers, EITs, consultants, and students — for preliminary and educational work. Every result comes with the complete worked solution: the governing equations, the numerical substitution, the stated assumptions, and the references behind them.
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Ohm's law — try it now
LiveResistance
60 Ω
Power
240 W
Worked solution
Live — try different values. Every calculator works exactly like this.
What a worked solution includes
The answer is the smallest part.
Most online calculators return a number and nothing else. Every calculator here returns the full record: the given quantities, the governing equation, the substitution, the result, the assumptions the method rests on, and the sources the formulas are drawn from. This is the voltage drop calculator at its default inputs — rendered live, not an image.
Voltage Drop Calculator
Three-phase feeder · 2/0 AWG copper · default inputs
Voltage drop (percent) 0.76%Within the 3% limit.
Worked solution
1. Conductor properties (per foot)
Representative values for THWN/THHN-class conductors in non-metallic conduit.
2. Effective impedance per foot
3. Voltage drop (three-phase, k = √3)
4. Voltage drop as a percentage
5. Receiving-end voltage
Given
- System
- Three-phase
- Conductor material
- Copper
- Conductor size
- 2/0 AWG
- Load current
- 80 A
- One-way run length
- 250 ft
- Source voltage
- 480 V
- Load power factor
- 0.9
- Maximum acceptable drop
- 3%
Assumptions
- Lagging (inductive) power factor assumed; a leading power factor would produce slightly less drop than shown.
- Conductor resistance and reactance are representative THWN/THHN values in non-metallic conduit, not a substitute for the governing code table.
- Balanced loading assumed for the three-phase case; steady-state conditions (not motor starting).
References
- NEC 210.19(A) Informational Note No. 4 and 215.2(A) Informational Note No. 2 — recommended voltage drop limits
- IEEE Std 141 (Red Book), Ch. 3 — Voltage Considerations
Change any input on the calculator page — the worked solution recalculates with it.
How these calculators are prepared
A number you can check beats a number you have to trust.
Built and verified by an engineer
ComputeVerse.ai is built and maintained by a practicing electrical engineer, using modern tools — including AI — as an assistant. The engineering judgment, checking, and review are human; the tools help produce it faster.
Checked against published examples
Each calculator's method, equations, and worked solution are checked against published examples from the references it cites where possible before it ships. If a calculation can't be sourced and reproduced, it doesn't go live.
Honest about limits
These are preliminary and educational calculations, and every page says so — the assumptions and limitations are stated where you can read them, not buried in fine print.
68 calculators · 10 categories · with citations
Download the Per-Unit Conversion Reference Card
A free quick-reference for practicing electrical engineers — base quantities, change of base, a worked example, and common base values. You'll also hear when new calculators are added: one or two emails a month, nothing else.
What you can calculate
From Ohm's law to fault current.
Calculators across 10 areas — the calculations that recur in design work, studies, and coursework. The library grows steadily; each new calculator meets the same standard.
Made for repeated use
Built to be bookmarked.
Free, no account
Open a calculator and use it. Nothing is gated behind a sign-up.
A record, not just a result
Save any calculation as a professional PDF — the worked solution, the figures and plots, assumptions, and references are all part of the printed page, suitable for a project file. Charts export as high-quality figures, and every calculation has a shareable link.
Readable as reference pages
Each calculator documents its method, its assumptions, and where its formulas come from — with interactive plots (Bode, pole-zero, K-maps, response curves) that make the behaviour visible, not just the number.
One thing to know before you rely on a result: these calculators are for preliminary engineering and educational use. How to use them responsibly