Transformer Sizing & Spare Capacity Calculator

A transformer sizing calculator that converts kW to kVA, applies demand and future spare allowance, and recommends a standard transformer size.

Inputs

Forms are empty on load. Use sample data to preview the workflow or enter your own project values.

Learn more

Formula logic, use cases, assumptions, and limits for this tool.

How this tool helps

Use this to avoid selecting a transformer that is either overloaded at day one or oversized without justification.

Assumptions and limits

This tool provides a planning-level result. It does not replace detailed engineering design, approved software, manufacturer data, authority requirements, or project specifications.

Typical use cases

  • Early estimation and tender support.
  • BOQ sanity checking and technical review.
  • Site discussion before final engineering verification.
  • Comparison of alternatives using consistent assumptions.

Result interpretation

Read the recommendation, warning, and confidence sections together. A result without warnings is still not an approval; it only means the entered values did not trigger built-in planning alerts.

Calculation methodology

Demand kW is converted to kVA, future spare is added, and the required kVA is divided by the preferred loading percentage.

Inputs are treated as planning assumptions. The calculator shows warnings when entered values fall outside practical thresholds or selected standard-profile limits.

View full methodology notes

Version history

  • v1.3.6-prelaunch: Added methodology, standard profile support, version notes, and direct PDF report download.
  • v1.3.5: Calculator page added with sample data, warnings, and print-ready report layout.

Stage 2 roadmap: optional saved projects, dashboards, and shared calculation history without forcing login for free use.

Trust and verification

Every result includes assumptions, warning logic, and a downloadable report. Final engineering decisions still need qualified review, local authority approval, manufacturer data, and project specifications.

Worked example

Use the sample data button to load a realistic scenario, then download the PDF report to review inputs, results, methodology, warnings, and disclaimers in one place.