Maximum Demand Calculator
Electrical systems rarely use every connected load at full power at the same time. A building may have lighting, air conditioning, sockets, motors, appliances, pumps, computers, or other equipment connected, but the actual peak load is usually lower than simply adding every rating together.
This Maximum Demand Calculator helps estimate the expected electrical maximum demand from your connected loads and demand factors. Enter the loads you expect to operate, apply an appropriate demand factor, and use the result to understand the estimated peak demand in kW.
For systems where power factor is relevant, the calculated demand can also be expressed in kVA.
Maximum Demand Calculator
Estimate electrical maximum demand from multiple connected loads, individual demand factors, power factor, and supply voltage.
| Load | Connected | Demand Factor | Estimated Demand |
|---|
What Is Maximum Demand?
Maximum demand is the highest electrical load that an installation is expected to draw during a relevant period of operation.
It is different from the total connected load.
Imagine a small commercial building with these connected loads:
Lighting: 15 kW
HVAC: 40 kW
Socket outlets: 20 kW
Kitchen equipment: 15 kW
Other equipment: 10 kW
The total connected load is:
15 + 40 + 20 + 15 + 10 = 100 kW
That does not necessarily mean the building will draw 100 kW simultaneously. Some equipment may be switched off, operating below its rated capacity, or reaching its peak at a different time.
Maximum-demand calculations attempt to account for this difference.
Demand and diversity calculations are commonly used in electrical design because connected load and actual coincident demand are not necessarily the same. Different standards and design practices use different rules, so the appropriate assumptions depend on the installation and jurisdiction.
Connected Load vs. Maximum Demand
These two terms are easy to confuse.
Connected load
Connected load is the combined rated power of the equipment or circuits being considered.
For example:
10 kW + 20 kW + 30 kW = 60 kW connected load
It represents what is connected, not necessarily what will be operating simultaneously.
Maximum demand
Maximum demand is an estimate or measurement of the highest simultaneous demand expected during operation.
If the 60 kW connected load is expected to reach only about 75% demand at the relevant peak:
60 × 0.75 = 45 kW
The estimated maximum demand would be 45 kW.
This distinction is important when planning electrical capacity because sizing everything from the raw connected load can produce a substantially different result from sizing around the expected coincident demand.
Maximum Demand Formula
The simplest form of the maximum demand calculation is:
Maximum Demand = Connected Load × Demand Factor
Where:
Maximum Demand is the expected peak load
Connected Load is the total installed load
Demand Factor represents the proportion expected to be demanded simultaneously
The demand factor can be written as:
Demand Factor = Maximum Demand ÷ Connected Load
So if a building has a 200 kW connected load and a maximum demand of 120 kW:
120 ÷ 200 = 0.60
The demand factor is 0.60, or 60%.
This relationship is also useful when you know the maximum demand and connected load but want to determine the implied demand factor.
How to Calculate Maximum Demand
There are several ways maximum demand can be estimated depending on what information is available.
Method 1: Connected load and demand factor
If you know the total connected load:
Maximum Demand = Connected Load × Demand Factor
Example:
Connected load = 250 kW
Demand factor = 0.65
250 × 0.65 = 162.5 kW
Estimated maximum demand:
162.5 kW
Method 2: Add individual diversified loads
For a more detailed estimate, divide the installation into load groups.
For example:
| Load | Connected Load | Demand Factor | Estimated Demand |
|---|---|---|---|
| Lighting | 20 kW | 0.80 | 16 kW |
| HVAC | 50 kW | 0.75 | 37.5 kW |
| Sockets | 30 kW | 0.50 | 15 kW |
| Motors | 40 kW | 0.60 | 24 kW |
Total connected load:
140 kW
Estimated diversified demand:
16 + 37.5 + 15 + 24 = 92.5 kW
The resulting estimate is therefore 92.5 kW.
The important point is that demand factors should not simply be chosen arbitrarily. Actual design calculations may use a relevant electrical standard, utility requirements, measured demand data, equipment characteristics, or engineering judgment.
What Is a Demand Factor?
A demand factor describes the relationship between maximum demand and connected load.
The formula is:
Demand Factor = Maximum Demand ÷ Connected Load
It is commonly expressed as either a decimal or percentage.
For example:
80 kW ÷ 100 kW = 0.80
or:
80%
A demand factor of 0.80 means the calculated maximum demand is 80% of the connected load.
Demand factor should not automatically be confused with diversity factor. They are related concepts, but they are used differently in electrical calculations. Some calculation methods apply demand factors to individual load groups, while other methods use diversity or coincidence assumptions to account for loads reaching their peaks at different times.
Maximum Demand Calculator: What Should You Enter?
For a basic calculation, you need:
Connected load
Demand factor
For a more detailed calculation, you may also need:
Individual load categories
Number of loads
Power rating of each load
Power factor
Supply voltage
Number of phases
Diversity assumptions
Coincidence assumptions
Historical demand data
The more detailed the installation, the more important the underlying assumptions become.