Built by electricians,
for the electrical contracting industry
The Electrical Toolbox is a free suite of BS 7671 calculation tools developed and maintained by Construct Software - a specialist technology company with deep links to electrical contracting. Every tool in the platform reflects real-world electrical engineering workflows, built by people who understand what these calculations are actually used for.
Industry-specific
Every tool is built specifically for electrical contracting and BS 7671 compliance work. No generic calculators - just the calculations you actually need on the job.
Standards-referenced
Calculations use the current wiring regulations: BS 7671:2018+A4:2026. Adiabatic equations, Zs limits, cable ratings and CPC requirements all reference the 18th Edition, Amendment 4.
Free, always
The full toolbox is offered free of charge as part of the Construct Software ecosystem. No trial limits, no premium tier, no catch - just tools that work.
The BS 7671 calculation platform that should have always existed
The Electrical Toolbox brings together the calculations that electrical professionals reach for most often - scattered across spreadsheets, reference books and one-off online calculators - into a single, consistent, browser-based platform. Free to use, immediately accessible and always available.
The platform covers 34 calculation tools spanning the full scope of electrical installation and testing work: adiabatic equations, cable sizing, maximum Zs lookup, voltage drop, demand and diversity, Ohm's Law, fault current analysis, earthing conductor sizing, R1+R2 temperature correction and more. Each tool is purpose-built: correct BS 7671 references, the right inputs, the right methodology and results that an engineer can rely on.
- 34 calculation tools covering BS 7671:2018+A4:2026 (18th Edition, Amendment 4)
- Cloud-based - accessible from any browser, any device, anywhere
- No installation, no subscription, no time limits
- Established equations and BS 7671 data tables throughout
- Account-based access via the shared Construct Software ID system
- Developed and maintained by Construct Software in the UK
A specialist software company rooted in the electrical contracting industry
Construct Software is a specialist software development company whose entire product portfolio is focused on the electrical contracting and building services sector. Unlike general-purpose software providers, every tool Construct Software builds is designed to address the specific technical, regulatory and operational challenges that electrical professionals face day to day.
The company develops in close partnership with industry-leading contractors - including Darke & Taylor Ltd, one of the largest MEP contractors in the south east of England - ensuring that products are shaped by real-world practice rather than theoretical requirements. The people building the software understand what it means to calculate a cable circuit, manage a portfolio of test certificates or commission a large electrical installation.
The Construct Software product suite now spans cable calculation, test and certification, compliance management, contractor compliance, temporary electrical systems, mechanical engineering tools and full-stack facilities management - covering the complete lifecycle of electrical and MEP installations.
More tools from Construct Software
The Electrical Toolbox is one part of a broader ecosystem. Each tool is independently useful, and together they cover the full breadth of electrical engineering, compliance and building services management.
SafetyCert
Cloud-based compliance management for electrical contractors - PAT testing, Minor Works, EICRs, document management and live compliance dashboards.
- PAT testing with asset registers and session locking
- Minor Works certificates to BS 7671
- EICR tracking with C1/C2/C3/FI observations
- Multi-site compliance dashboard and expiry alerts
CableSpec Pro
Professional-grade cable calculation for large projects. Manage entire distribution boards and circuit schedules with diversity and fault level analysis.
- Project-level multi-circuit management
- Distribution board scheduling
- Full diversity and fault level analysis
- Comprehensive project calculation reports
ElectraCert
Produce compliant Electrical Installation Certificates, Minor Works Certificates and Condition Reports to the latest wiring regulations.
- EIC, MEIWC and EICR certificate production
- Compliant with BS 7671:2018+A4:2026
- Schedule of inspections and test results
- PDF generation and client distribution
ContractorCompliance
Manage contractor insurances, qualifications and certifications, with a self-service portal for contractors to maintain their own credentials.
- Insurance and certification expiry tracking
- Contractor self-service upload portal
- Accreditation scheme verification (NICEIC, NAPIT, ECA)
- Compliance status dashboard
FacilitiesMaster
A comprehensive FM platform for managing assets, PPM schedules, reactive jobs, contractors and compliance documentation across property portfolios.
- Asset register and lifecycle management
- PPM scheduling and job tracking
- Contractor management and attendance records
- Multi-site portfolio management
TESCert
Purpose-built for events, media and entertainment - produces BS 7909 certification documentation for temporary electrical systems.
- TES certificates compliant with BS 7909
- Designed for events and temporary installations
- Engineer declaration and sign-off workflow
- PDF generation for venue compliance
Ready to get started?
Create your free Electrical Toolbox account and get instant access to all 34 BS 7671 calculation tools.