Calculator Inputs
Formula Used
General load: area × VA per square foot + small appliance circuits × 1,500 VA + laundry circuits × 1,500 VA.
Optional dwelling load: total dwelling connected VA × multifamily demand factor.
Standard style dwelling load: demanded general load + demanded fixed appliances + range demand + dryer demand + larger HVAC load + motor load.
House load: common base load × selected factor + elevator motors + pump motors + 25% of the largest motor.
Total VA: dwelling demand + house demand. Single phase current = VA ÷ volts. Three phase current = VA ÷ (1.732 × volts).
How to Use This Calculator
- Select optional or standard style calculation.
- Enter dwelling units, service voltage, and phase.
- Add floor area, small appliance circuits, and laundry circuits.
- Enter nameplate VA for ranges, dryers, fixed appliances, and HVAC.
- Add common area, motor, pump, EV, and fire system loads.
- Adjust demand factors only when your adopted rules allow them.
- Press calculate, then review kVA, amperes, and service size.
Example Data Table
| Example item | Input | Purpose |
|---|---|---|
| Dwelling units | 12 units | Sets the multifamily demand range. |
| Area per unit | 950 sq ft | Builds general lighting load. |
| Range load | 12,000 VA per unit | Represents cooking equipment. |
| Dryer load | 5,000 VA per unit | Applies minimum dryer allowance. |
| Common lighting | 8,000 VA | Adds house load after dwelling demand. |
| Spare margin | 20% | Shows planning capacity above demand. |
Multi-Family Service Load Planning
A multifamily service calculation starts with each dwelling unit. The goal is simple. List every normal connected load. Then reduce permitted groups with demand factors. This gives a service load that is practical, yet still conservative for construction review.
Dwelling Unit Inputs
The floor area supports general lighting and general receptacle allowance. Small appliance circuits add kitchen and dining loads. Laundry circuits add separate allowance. Fixed appliances add nameplate ratings. Ranges and dryers may need their own demand settings. Heating and cooling are compared. Use the larger value, not both, unless loads can operate together.
Article 220 Style Method
This calculator includes an optional multifamily method. It totals the dwelling unit loads first. Then it applies a unit count demand factor. Larger buildings usually receive lower diversity factors. This reflects the chance that every apartment will not peak at the same moment. The tool also includes a standard style method. That method demands the general load first. It then adds demanded appliance, range, dryer, motor, and HVAC loads.
House Loads
House loads are separate from apartment loads. They include corridors, stairs, parking lights, pumps, elevators, fire systems, office outlets, common laundry, and EV charging. These loads are added after the dwelling demand. Continuous portions can be multiplied by a selected factor. Motor loads can include an extra allowance for the largest motor.
Design Review
The final result is shown in volt amperes, kVA, and amperes. The amperes are calculated from the selected service voltage and phase. A spare margin can be added for future growth. A rounded service rating is also suggested. This rounded value is only a planning aid. Final conductor, equipment, and overcurrent ratings must follow the adopted code, temperature limits, utility rules, and local approval.
Better Inputs Create Better Outputs
Use real nameplate data where possible. Avoid guessing large appliance loads. Separate dwelling and house loads clearly. Confirm whether the optional method is allowed for the project. Keep notes for the authority having jurisdiction. Review the neutral load, heating type, range demand, dryer demand, and motor contribution. A clean calculation reduces redesign time. It also helps compare service sizes before drawings are finalized.
Save each project input set when records are needed for estimating, bidding, review meetings, and later coordination with electrical designers.
FAQs
What does this calculator estimate?
It estimates multifamily electrical service demand. It combines dwelling loads, common house loads, motors, HVAC, ranges, dryers, and spare capacity into kVA and amperes.
Is this a final code approval tool?
No. It is a planning and estimating tool. Final service design must be checked by qualified professionals and approved under the adopted local electrical code.
What is the optional multifamily method?
It totals dwelling unit connected loads and applies a demand factor based on the number of units. House loads are then added separately.
When should I use the standard style method?
Use it when you want separate demand control for general loads, fixed appliances, cooking loads, dryers, motors, and HVAC. It is also useful for comparisons.
Why is the dryer load at least 5,000 VA?
The calculator uses 5,000 VA as the minimum household dryer load. If a dryer nameplate is higher, enter the higher value.
How are heating and cooling handled?
The calculator compares heating and cooling per dwelling unit. It uses the larger value, unless your project has loads that must operate at the same time.
What are house loads?
House loads serve common areas. They can include corridors, stair lighting, exterior lighting, pumps, elevators, common laundry, fire systems, and parking equipment.
Why is there a largest motor adder?
Motor groups often need extra allowance for the largest motor. This calculator adds 25% of the largest entered motor as a planning adjustment.
What does neutral factor mean?
The neutral factor estimates the portion of total demand carried by the neutral. It is only a planning value and should be verified by code rules.
Why add spare capacity?
Spare capacity helps compare future-ready service sizes. It can account for tenant changes, EV additions, equipment changes, or design uncertainty.
Can I export the result?
Yes. After submitting the form, use the CSV or PDF button above the form. The export includes the detailed result table.