Peak Demand Calculator

A peak demand calculation estimates the highest coincident load expected from an installed electrical load. The calculator produces Peak demand in kW by applying the entered Diversity factor to the total Connected load. It also shows Spare capacity and Utilization against the entered Service capacity.

This result is useful during preliminary service-load review, feeder planning, electrical distribution studies, equipment expansion screening, and early design coordination. A connected load total can include equipment that is installed or available to operate but not expected to run simultaneously. The diversity factor reduces that total to an estimated coincident demand.

For example, a facility may have 100 kW of connected HVAC, lighting, receptacle, process, and motor load, while historical operating patterns suggest that only 80 percent is expected to be coincident at peak. The calculated peak demand is then 80 kW rather than the full 100 kW connected load.

Calculation Inputs

Input	Unit	Electrical meaning
Connected load	kW	Total installed load included in the screening calculation
Diversity factor	%	Percentage of connected load expected to operate coincidentally at peak
Service capacity	kW	Available service capacity used to compare against the estimated peak demand

Connected load is not necessarily the same as calculated service load, demand load, measured interval demand, or utility billing demand. It is the starting load total selected for this planning calculation.

Diversity factor represents expected non-coincident operation. An 80% diversity factor means the peak demand is estimated at 80% of connected load. A 100% diversity factor assumes all included connected load is coincident at peak.

Service capacity is entered in kW, so it should represent capacity on the same real-power basis as the connected load and peak demand. Do not compare kW demand directly against equipment ratings expressed only in amperes, kVA, or horsepower without first establishing a consistent basis.

Peak Demand Formula

The calculator uses the entered values directly:

\(\displaystyle \text{peak demand kW} = \text{connected load kW} \times \frac{\text{diversity factor}}{100}\)

It then compares that result with service capacity:

\(\displaystyle \text{spare capacity kW} = \text{service capacity kW} - \text{peak demand kW}\)

\(\displaystyle \text{utilization percent} = \frac{\text{peak demand kW}} {\text{service capacity kW}} \times 100\)

The displayed Diversity factor used confirms the percentage applied to the connected load.

Calculation Example

Enter the following values:

Field	Entered value
Connected load	100 kW
Diversity factor	80%
Service capacity	125 kW

The estimated peak demand is:

\(\displaystyle 100\text{ kW} \times \frac{80}{100} = \text{80 kW}\)

The remaining service capacity is:

\(\displaystyle 125\text{ kW} - 80\text{ kW} = \text{45 kW}\)

Service utilization is:

\(\displaystyle \frac{80\text{ kW}}{125\text{ kW}} \times 100 = \text{64\%}\)

The calculator result is therefore:

Result	Value	Interpretation
Peak demand	80 kW	Estimated coincident demand based on the entered diversity factor
Spare capacity	45 kW	Capacity remaining after the estimated peak demand
Utilization	64%	Estimated portion of service capacity used at peak
Diversity factor used	80%	Confirmed factor applied to connected load

Electrical Planning Use

Peak demand is commonly reviewed before adding major loads or modifying distribution equipment. A preliminary kW result can help identify whether a service, feeder, transformer, switchboard, panelboard, or generator may require a more detailed review.

Typical applications include:

• Screening an existing service before adding EV charging, HVAC equipment, process equipment, or tenant loads.
• Estimating whether a feeder may carry an anticipated operating load before detailed conductor ampacity selection.
• Comparing alternative load-management assumptions during early design.
• Identifying whether measured interval data should be collected before approving an expansion.
• Establishing an initial load basis for voltage-drop review, transformer loading, and distribution capacity planning.

The kW result does not directly select an AWG or kcmil conductor size. Conductor sizing requires current, system voltage, phase configuration, power factor where applicable, conductor insulation temperature rating, terminal rating, ambient-temperature correction factor, adjustment factor for current-carrying conductors, and any required continuous-load treatment.

Likewise, the result does not establish raceway fill, conduit layout, equipment working space, overcurrent protection, or motor branch-circuit calculations. Those decisions depend on the actual installation and equipment characteristics.

Field Verification

Use a documented basis for the entered Connected load. Include only loads within the scope of the review, identify whether values are nameplate ratings or calculated operating loads, and avoid mixing unrelated demand assumptions in one total.

Select the Diversity factor from a defensible operating assumption. A diversity factor based on actual interval data, documented schedules, process sequencing, building occupancy, or an engineered load study is stronger than an arbitrary percentage. Loads with shared operating conditions—such as electric heat during a cold-weather event or multiple EV chargers during a charging window—may be more coincident than expected.

A positive Spare capacity indicates that the calculator’s estimated peak demand is below the entered service capacity. It does not confirm that the service can accept new load. Verify the actual service equipment rating, utility transformer capability, measured demand profile, feeder and service conductor ampacity, protective-device ratings, voltage drop, available fault current, and applicable utility requirements.

Calculation Boundary

The worksheet provides a planning estimate only. It does not perform an interval-data review, coincidence study, demand ratchet analysis, tariff review, utility service approval, or final electrical service calculation.

Final design and installation decisions require the applicable code calculation method, actual equipment nameplates, system characteristics, conductor and termination ratings, load classifications, site conditions, and review by the authority having jurisdiction (AHJ) where required.