How do kVA, kW and power factor affect your charging capacity?

kW measures active power, while kVA measures apparent power. Power factor connects them: kW equals kVA multiplied by power factor [S1]. For an assumed 100 kVA supply at a power factor of 0.95, that is 95 kW. Your existing building demand still needs to be allowed for before sizing chargers. Checked October 2026.

Last checked 16 October 2026

What is the difference between kVA and kW?

A kilowatt, or kW, measures active power. A kilovolt-ampere, or kVA, measures apparent power. Power factor is the ratio of active power to apparent power. It explains why an equipment schedule expressed in kW cannot always be compared directly with a connection offer expressed in kVA [S1].

UK Power Networks says it uses kVA for generation and distribution equipment sizing, while electricians commonly work in watts and kilowatts [S2]. Neither unit is a count of charging sessions. Start your project brief by writing the unit beside every figure, including any number copied from an old survey or connection letter.

For a pub, factory or depot, the useful question is whether the proposed charging demand fits alongside the building’s demand. Read how much power your site has before assuming that a supply rating is all available for chargers.

How do you convert kVA to kW using power factor?

Use kW = kVA × power factor. To work in the other direction, use kVA = kW ÷ power factor [S1]. The following figures are assumed inputs for arithmetic only, not measured conditions at your site.

Conversely, an assumed 80 kW load at 0.95 power factor corresponds to approximately 84.2 kVA: 80 ÷ 0.95. Ask your electrical designer to supply the relevant operating power factor. A convenient default in a spreadsheet is not evidence about the installed equipment [S1].

How are power and energy different when planning charging?

A kilowatt-hour, or kWh, measures energy. An assumed constant 10 kW load running for 2 hours uses 20 kWh: 10 × 2 = 20. This is a unit calculation, not a prediction of a vehicle’s charging performance [S1].

Keep separate spreadsheet columns for maximum power, energy needed and time available. A vehicle needing a top-up during a long shift creates a different design brief from a vehicle returning briefly between delivery rounds. Record arrival and departure windows instead of asking only for the highest charger rating in the catalogue.

The kW and kWh guide explains the energy calculation. Use the resulting requirements to discuss charger numbers and speed with your installer, as the government connection guidance recommends [S5].

Why are supply limits and transformer ratings expressed in kVA?

Apparent power matters to equipment sizing because the electrical system must carry the current associated with the load. Power factor describes the relationship between that apparent power and active power [S1]. This is why changing the unit label on a charger schedule does not establish the required connection size.

UK Power Networks describes maximum import capacity as the maximum power your property can draw from its network, measured in kVA [S4]. Keep the agreed limit, transformer rating and measured demand as distinct records. Ask your designer to explain any differences before relying on spare capacity.

Bring the latest connection agreement to the survey. An old installation drawing may describe equipment without establishing what your current agreement permits.

How should you assess spare capacity for EV chargers?

Prepare a load schedule covering existing operations and the proposed charging service. Include equipment that has been ordered but is not yet running. Ask the designer to explain which loads coincide and how that changes the application. The government advises early network discussions for workplaces and depots adding multiple chargers [S5].

Request these outputs in the survey report:

• Existing demand evidence, including when the site is busiest.
• The assumed charging demand and the reason for that assumption.
• The power factor used in converting proposed demand.
• The proposed import limit and how the controls enforce it.
• The effect of later expansion on the design.

Compare dynamic load management with an upgrade. Ask for the charging service each option can actually deliver, rather than comparing the connection cost alone.

Will power factor correction remove the need for an upgrade?

Do not authorise correction equipment from a conversion table. Ask for measurements and a design recommendation. UK Power Networks publishes power factor conditions for its connections, including a minimum of 0.95 unless otherwise agreed and qualifications about reactive energy [S3]. Your connection’s own terms need checking.

For illustration, supplying an assumed 80 kW at power factor 0.80 requires 100 kVA; at 0.95 the calculation gives about 84.2 kVA [S1]. That calculation identifies a possible question for the designer. It does not establish that correction is appropriate, that capacity is available or that your electricity bill will fall.

Ask for the proposed solution’s installed price, inspection needs and measured acceptance criteria. Keep a capacity study separate from any income forecast.

What should you send with a connection enquiry?

Provide your site plan, current agreement, equipment schedule and charging requirements. Mark which details are confirmed and which are assumptions. The network operator needs to understand the scale and location of the requested connection; government guidance describes these as application inputs [S5].

Read the DNO application guide. DNO means distribution network operator: the organisation responsible for the local electricity network. Ask the installer to identify the DNO and explain which submissions and permissions are included in its scope [S5].

What should you do next?

Prepare a brief using the site survey guide, then get matched with an installer that covers your area. Include any known kVA limit and describe the charging service you need.

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