Free tool

EV charging capacity calculator

The EV charging capacity calculator estimates your site's spare electrical capacity, how many chargers fit at full rate, and how many cars load management could recharge overnight. Enter your supply, measured peak and daily driving needs for an indicative comparison to discuss with your electrical designer.

What could your spare capacity serve?

Start with the example values, then enter your site numbers. Results update as you type.

Your site

01 / Supply and existing load

Use the supply shown on your site drawings or confirmed by your electrician.

Supply rating, 1–5,000 A per phase.

From your electricity retailer's interval data, a power-quality logger, or a meter on the main switchboard. Use the highest phase reading; 0 A up to the supply rating.

Reserve 0–30% of the supply rating before allocating EV capacity.

02 / Bays and nightly energy

A single-phase supply permits only the 7.4 kW option.

1–500 whole bays, with one vehicle in each bay.

Average distance to replenish each night, 1–1,000 km.

Vehicle energy use, 1–100 kWh/100 km. Use a figure suited to your vehicles.

Time vehicles are connected, 1–24 hours. The default is nine hours overnight.

03 / Demand charge, optional

Leave blank to hide this estimate. Enter 0–10,000 in the unit below from your site's tariff.

Calculations run in your browser. These inputs are never sent, saved or used for analytics.

Indicative results

60A / phase

Spare current after margin

41.4kW

Total spare power
Where the supply goes, per phase
  • Existing peak
  • Spare
  • Margin

Dashed line: usable limit of 180 A. The same conservative peak is applied to each phase.

Without load management

3/ 20

Chargers that fit at full rate

Whole chargers within each phase budget, capped at the number of bays.

With load management

20/ 20

Cars replenished per night, by energy budget

An energy estimate assuming the spare capacity can be used throughout the window.

Energy available in the window
372.6 kWh
Energy needed for all bays
136 kWh
Energy needed per car
6.8 kWh
Mean current per bay, per connected phase
9 A

Energy headroom

The energy estimate covers all bays with at least 20% headroom. Check the assumptions with your electrical designer.

Assumptions behind this estimate

  • 230 V phase-to-neutral, power factor 1 and a constant existing peak throughout the window.
  • Identical driving needs for every bay, with all vehicles connected for the entire window. Charging losses are excluded.
  • Single-phase chargers are spread across supply phases. The current figure is an ideal average; uneven bay counts and phase loads can limit individual bays sooner.
  • The energy budget uses all spare supply power. It does not cap energy at charger or vehicle limits, or simulate the 6 A floor, queues or time lost while switching. It can overstate deliverable energy, especially with few bays or little spare current.
  • The mean current is a share of the supply budget, not a charger setting; each charger still has its own current limit.

The method

How the numbers work

Start with spare amps

Multiply the supply rating by one minus the margin percentage, then subtract the measured existing peak. Anything below zero becomes zero. Multiply spare amps by 230 V and the number of phases, then divide by 1,000 to get kW.

Count whole chargers

Divide spare amps by the charger's current per phase and round down. For single-phase chargers on a three-phase supply, multiply that count by three. The result cannot exceed your bay count.

Compare nightly energy

Multiply bays by daily kilometres and kWh per 100 km, then divide by 100. Compare that need with spare kW multiplied by hours connected. Divide available energy by each car's need and round down to count whole replenishments.

The ideal mean current divides spare amps across all bays. For single-phase chargers spread over three phases, it shares three phase budgets. An energy budget at least 20% above the nightly need is shown as having headroom; a smaller surplus is tight, and a deficit is a shortfall.

The optional demand estimate subtracts the managed EV cap from all bays' combined rated kW, with a minimum of zero. At power factor 1, that difference approximates kVA. Multiply by a monthly dollar rate and 12, or by a daily cent rate divided by 100 and 365, for the indicative annual value.

AS/NZS 3000 clause 2.2.2 lists calculation, assessment, measurement and limitation as ways to determine maximum demand. The Electric Vehicle Council's 2024 guidance, Determining maximum demand for an apartment complex with EV chargers, treats a load-management system as creating a definite duty cycle under the assessment method. Choosing and applying the method is always the electrical designer's call.

Read the guide to maximum demand and EV charging, or explore charging for commercial and industrial sites.

From estimate to site control

How does Edge CSMS manage the available current?

Nohmad Edge CSMS measures the non-EV load and re-allocates the remaining capacity every 10 seconds. It enforces limits per phase where meters and charger phase mappings exist; otherwise it uses the worst phase.

At the incoming supply, instantaneous and rolling-average demand caps operate in kW and need a meter reporting voltage there. The calculator's approximate kVA comparison is a separate tariff illustration.

If meter data goes stale, after 60 seconds by default, the system enters fail-safe: active chargers drop to their configured safe current, new sessions start only at safe current, and a critical alarm is raised.

Load management sits on top of your protection, never instead of it — breakers remain the last line.

Explore Nohmad Edge CSMS

Questions

Before you use these numbers

Where do I find my existing peak demand?

Ask for your electricity retailer's interval data, use a power-quality logger, or have an electrician read a meter on the main switchboard. This tool needs amps per phase. Ask your electrical designer to interpret kW or kVA data and choose a representative measurement period.

Does this tell me how many chargers I can install?

It estimates how many selected chargers fit at full rate and how many vehicles the spare energy could replenish. Cable ratings, boards, phase allocation, vehicle limits and the site design still need assessment by your electrical designer. It is not an installation design.

Why can load management serve more bays?

Every vehicle may not need a full-rate charge throughout the night. Sharing the spare current over a longer window can meet daily energy needs across more bays. The result depends on building load, driving distance, time connected and the vehicles' charging limits.

What happens below 6 A per bay?

If the mean allocation falls below 6 A, not all bays can charge together: some would pause until capacity frees up. If a phase has less than 6 A spare, pausing alone cannot create enough current to charge on it. The calculator's energy estimate does not simulate this behaviour.

Is the demand-charge figure a predicted saving?

No. It is an indicative annual value using the rate you enter, power factor 1 and a simultaneous full-rate arrival peak. Networks measure demand over 15- or 30-minute windows and many look back 12 months. The site's tariff, timing and existing peak determine any actual change in charges.

Are my inputs sent to Nohmad?

No. The calculator runs in your browser and does not send, store or track its inputs. The contact link opens a separate enquiry form; you choose which numbers to share there.

Want a second pair of eyes on the result?

Tell us about your supply, existing peak and vehicles. Choose what to share in the enquiry form; your calculator inputs are not attached.

Send us your numbers