Free Electrical Engineering Calculators — Complete List [2026]
A comprehensive, categorised list of every free electrical engineering calculator available online in 2026. Cable sizing, voltage drop, arc flash, motor sizing, conduit fill, and more.
Engineers search for free calculators constantly — and most results are either ad-laden single-purpose tools, outdated Java applets, or thinly veiled lead generation forms. This page is a genuine reference: every notable free electrical engineering calculator available online in 2026, categorised by calculation type, with honest notes on what each tool covers and where its limitations are.
Last updated: March 2026.
Cable Sizing Calculators
Cable sizing is the most searched-for electrical calculation. These tools determine conductor size based on current rating, voltage drop, and short circuit withstand.
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | AS/NZS 3008, BS 7671, IEC 60364, NEC | 5 calcs/day, watermarked reports | Only tool covering all 4 major standards for free. 27 calculators total. Offline PWA. |
| ELEK Cable Pro | AS/NZS 3008, BS 7671, IEC 60364 | 6 calcs/day | Strong Australian tool. No NEC. Premium features locked behind paid tiers. |
| ElectricalOM | BS 7671, IEC 60364 | Limited free access | Nexans-backed. Good BS 7671 implementation. No AS/NZS or NEC. |
| Cablizer (Nexans) | IEC 60364 | Free with registration | Manufacturer-specific cable data. IEC only. |
| Southwire Voltage Drop | NEC | Fully free | Single-purpose voltage drop calculator. NEC wire sizes only. |
| Cerrowire Calculator | NEC | Fully free | Basic NEC wire sizing. Limited features. |
Recommendation: For multi-standard cable sizing, ECalPro is the only free option covering AS/NZS, BS, IEC, and NEC. For NEC-only quick checks, Southwire's calculator is simple and free without registration.
Voltage Drop Calculators
Voltage drop is often calculated alongside cable sizing, but standalone tools exist for quick checks.
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | AS/NZS, BS 7671, IEC, NEC | 5 calcs/day | Full voltage drop with derating, installation methods, and report output. |
| Southwire Voltage Drop | NEC | Fully free | Quick NEC voltage drop check. No derating factors. |
| Olex Cable Calculator | AS/NZS | Fully free | Manufacturer tool from Nexans. AS/NZS only. |
| Schneider Voltage Drop | IEC | Free with registration | Part of Schneider's online toolbox. |
Arc Flash Calculators
Arc flash calculation tools are less common in free form because of the complexity and liability involved.
| Tool | Method | Free Limits | Notes |
|---|---|---|---|
| ECalPro | IEEE 1584-2018 | 5 calcs/day | Full IEEE 1584-2018 implementation with incident energy and PPE category. |
| ELEK Cable Pro | 5 methods (IEEE 1584, ENA, DGUV, Stokes, Max Power) | 6 calcs/day | Most comprehensive free arc flash tool. Includes DC arc flash. |
| Arcflash.info | IEEE 1584-2002 | Fully free | Older 2002 edition. No 2018 update. Useful for quick estimates only. |
Recommendation: For serious arc flash studies, ELEK's free tier offers the most methods. For IEEE 1584-2018 compliance, ECalPro's free tier is sufficient for occasional calculations.
Arc Flash Calculation Caution
Arc flash calculations have direct safety implications — they determine PPE requirements that protect workers from potentially fatal burns. Free tools should be verified against known reference results before being used for actual PPE selection. Never rely on a single tool without verification.
Short Circuit / Fault Level Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | IEC 60909, AS/NZS 3008, BS 7671, NEC | 5 calcs/day | Full fault calculation with cable withstand check. |
| ELEK Cable Pro | IEC 60909, AS/NZS | 6 calcs/day | Includes protection coordination on paid tiers. |
| Easy Power (demo) | ANSI/IEEE | Limited demo | Desktop software with limited free demo. |
Motor Sizing and Starting Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | IEC, NEC, AS/NZS | 5 calcs/day | Motor starting current, cable sizing, protection sizing. |
| jCalc | AS/NZS | Paid only | Good motor calculators but no free tier. |
| ABB Motor Sizing | Manufacturer-specific | Free with registration | ABB motor selection tool. Not standards-based. |
Conduit Fill Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | NEC Chapter 9, AS/NZS 2053, BS 7671, IEC | 5 calcs/day | Multi-standard conduit fill with all four codes. |
| Southwire Conduit Fill | NEC | Fully free | Quick NEC Chapter 9 conduit fill check. |
| Rack-A-Tiers | NEC | Fully free | Simple NEC conduit fill calculator. |
Maximum Demand Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | AS/NZS 3000, BS 7671, IEC | 5 calcs/day | Full maximum demand with diversity factors. |
| ELEK Cable Pro | AS/NZS 3000 | 6 calcs/day | Australian maximum demand calculation. |
Earthing / Grounding Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | AS/NZS 3000, BS 7671, IEC, NEC | 5 calcs/day | Earth electrode resistance, earth fault loop impedance. |
| Copper Development Association | BS 7671 | Fully free | Basic earth electrode sizing. BS 7671 only. |
Lighting Calculators
| Tool | Standards | Free Limits | Notes |
|---|---|---|---|
| ECalPro | Various | 5 calcs/day | Lighting circuit sizing, not photometric design. |
| DIALux | Manufacturer-agnostic | Fully free | The industry standard for photometric design. Not a circuit calculator. |
| Relux | Manufacturer-agnostic | Fully free | Alternative to DIALux for lighting design. |
Note: DIALux and Relux are lighting design tools (photometric calculations), not electrical circuit calculators. They determine light levels, not cable sizes. Use them alongside a cable sizing tool, not instead of one.
Unit Conversion and Reference Tools
| Tool | Purpose | Free Limits |
|---|---|---|
| RapidTables | Electrical unit conversions | Fully free |
| AllAboutCircuits | Ohm's law, power, impedance | Fully free |
| CalcTool | General engineering calculations | Fully free |
What "Free" Actually Means
Not all free tiers are equal. Here is what limitations to expect:
| Limitation Type | ECalPro | ELEK | ElectricalOM |
|---|---|---|---|
| Daily calc limit | 5/day | 6/day | Varies |
| Report watermark | Yes (removable with Pro) | N/A | N/A |
| All calculators accessible | Yes (all 27) | Limited | Limited |
| Registration required | Yes | Yes | Yes |
| Offline access | Yes (PWA) | No | No |
| Data saved to account | Yes | Yes | Varies |
What You Get Free with ECalPro
ECalPro's free tier includes all 27 calculators across 4 international standards, with no time limit. The limitations are: 5 calculations per day, watermarked PDF reports, and 3 project slots. Every calculation uses the same verified engine as paid tiers — the results are identical.
How to Evaluate a Free Calculator
Before trusting any free calculator on a real project:
- Run a known calculation — Use inputs from a project where you know the correct answer (from hand calculation or a verified reference). Compare results.
- Check the standard edition — Some tools reference outdated standard editions. Verify the tool specifies which edition it implements.
- Look for intermediate steps — A tool that only shows the final cable size without showing the derating factors applied, the current rating table used, or the voltage drop calculation is a black box. You cannot verify what you cannot see.
- Check clause references — Professional tools cite specific standard clauses (e.g., "BS 7671 Table 4D1A, Column 6"). If a tool does not tell you which table it used, you cannot verify the result.
- Test edge cases — Enter a very long cable run (200m+), a high ambient temperature (45 degrees C+), or a heavily grouped installation (12+ circuits). These stress tests reveal whether the tool handles derating correctly or takes shortcuts.
Frequently Asked Questions
Are free electrical calculators accurate enough for professional use?
Free tiers from reputable platforms (ECalPro, ELEK) use the same calculation engine as their paid versions. The calculations are identical — free tiers limit report formatting, daily usage, or collaboration features, not accuracy. Single-purpose free tools (like Southwire) are also accurate for their specific scope but lack the depth of multi-standard platforms.
What is the best free cable sizing calculator?
For multi-standard coverage, ECalPro's free tier is the most comprehensive — it covers AS/NZS 3008, BS 7671, IEC 60364, and NEC with 5 free calculations per day. For NEC-only quick checks, Southwire's voltage drop calculator is fully free without daily limits. For Australian work, ELEK's free tier offers 6 calculations per day.
Can I use free calculators for building permits and code compliance?
The calculation methodology in reputable tools complies with the referenced standards. However, the responsibility for code compliance rests with the design engineer, not the software. Free tools do not reduce your professional liability — they provide the same calculations that a paid tool or hand calculation would produce.
Why do some free calculators show different results?
Different results usually come from different standard editions, different assumptions about installation conditions, or different treatment of derating factors. For example, some tools assume a default ambient temperature of 30 degrees C while others use 25 degrees C or 35 degrees C. Always check which standard edition and which default assumptions a tool uses.
Is there a completely free tool with no daily limits?
Southwire and Cerrowire offer NEC-specific calculators with no daily limits, but they are single-purpose tools (voltage drop or wire sizing only). For full multi-standard cable sizing with derating, short circuit checks, and professional reports, all comprehensive tools impose some form of free-tier limitation.
Related Resources
- 7 Best Cable Sizing Calculators Compared [2026]
- Cable Sizing: Calculator vs Excel — 7 Reasons to Switch
- ECalPro vs Excel: Why Engineers Are Moving to Cloud Calculators
- View all calculators
Try the Cable Sizing Calculator
Free online tool — no signup required
Lead Electrical & Instrumentation Engineer
18+ years of experience in electrical engineering at large-scale mining operations. Specializing in power systems design, cable sizing, and protection coordination across BS 7671, IEC 60364, NEC, and AS/NZS standards.