Transformer Sizing Calculator: kW to kVA & Rated Amps

Transformer Sizing Calculator

Connected electrical input load (kW)Power factorDemand factor (%)Planning reserve (%)Candidate nameplate rating (kVA)Secondary line-to-line voltage (V)

Calculations run in your browser. Sharing puts numeric assumptions in the link. No registration required.

Formula

Operating kVA = kW × (demand % ÷ 100) ÷ PF. Planning requirement = operating kVA × (1 + reserve % ÷ 100). Rated secondary current = candidate kVA × 1,000 ÷ (√3 × V).

Worked example

1,000 kW at PF 1, 100% demand and 0% reserve needs 1,000 kVA before project-specific allowances. A 1,000 kVA candidate at 480 V has a rated current of about 1,203 A.

What this calculation does not cover

For balanced three-phase loads. The reserve is a user-selected planning assumption, not a code requirement. Harmonics, ambient temperature, altitude, cooling, overload duty and local requirements need separate manufacturer/engineering review.

Sources & further reading

Schneider Electric Electrical Installation Guide: apparent power ↗

Sources checked October 8, 2026. Follow the source for revisions and regional product details.

Using the result responsibly

Keep a record of the input units and operating assumptions. A change in one input can make two apparently similar equipment options impossible to compare. Export the scenario before reviewing it with your engineer or equipment manufacturer.

Educational planning only. These tools do not replace a licensed professional’s design, a manufacturer selection study or applicable local requirements.

Transformer Sizing Calculator