Calculator Inputs
Formula Used
Gross area = floor area per level × levels.
Net area = gross area − excluded area.
Area load = net area × lighting density.
Fixture load = fixture count × fixture watts × (1 + driver loss %) ÷ power factor.
Selected load = chosen method value or the greater value.
Final VA = selected load × demand factor × continuous factor × spare factor.
Single phase amps = final VA ÷ voltage.
Three phase amps = final VA ÷ (voltage × √3).
Estimated circuits = final VA ÷ usable circuit VA, rounded upward.
How To Use This Calculator
- Select the commercial occupancy type.
- Enter the project lighting density.
- Add floor area, levels, and excluded spaces.
- Add fixture schedule data when known.
- Choose area, fixture, or higher value method.
- Set demand, continuous, and spare factors.
- Enter voltage, phase, circuit ampacity, and loading limit.
- Press the calculate button to view results.
- Use the CSV or PDF button for exports.
Example Data Table
| Example | Area | Density | Fixtures | Voltage | Expected Use |
|---|---|---|---|---|---|
| Office tenant | 10,000 sq ft | 3.5 VA/sq ft | 240 at 32 W | 208 V three phase | Early panel sizing |
| Warehouse bay | 25,000 sq ft | 1.0 VA/sq ft | 180 at 90 W | 480 V three phase | Feeder review |
| Retail area | 7,500 sq ft | 3.0 VA/sq ft | 320 at 24 W | 208 V three phase | Tenant allowance |
Commercial Lighting Load Planning
A commercial lighting estimate starts with usable floor area. The area is multiplied by a lighting density. That density is usually stated in volt-amperes per square foot. Designers often select it from adopted electrical rules. They may also use an approved energy model. This calculator keeps that input editable. That makes the result flexible for many building types.
Why Load Details Matter
Lighting may run for long business hours. That can make it a continuous load. Many designs add a continuous load factor. A common planning factor is one hundred twenty five percent. The tool also adds spare capacity. Spare capacity helps future tenant changes. It also helps when fixtures are added later. The final volt-ampere result supports panel planning. It also supports feeder and branch circuit review.
Area Method And Fixture Method
The area method is fast. It works during early design. Enter floor area, levels, and excluded areas. Then enter the required lighting density. The fixture method is more detailed. It uses fixture count, wattage, power factor, and driver loss. The calculator can compare both values. It can use the higher value for conservative planning. This is useful before schedules are fully coordinated.
Current And Circuit Planning
After load is found, voltage affects current. Single phase current equals volt-amperes divided by voltage. Three phase current uses the square root of three. Circuit capacity depends on breaker size. It also depends on the selected loading limit. The calculator estimates required circuit count. This number is only a planning guide. Final circuits need layout review and local approval.
Good Use In Commercial Projects
Use the result during schematic design. Check it again during design development. Update inputs when fixture schedules change. Review adopted rules before final submission. Coordinate lighting loads with panels, feeders, and emergency systems. Separate general lighting from receptacles and special equipment. Keep notes for assumptions and tenant allowances. Clear assumptions reduce revisions during plan review. Accurate load planning keeps commercial electrical designs safer.
Review Workflow
Start with the adopted occupancy type. Confirm the measured area source. Use the density accepted by the authority. Add fixture data when it becomes available. Compare calculated load against panel schedules. Check spare allowance with the owner. Document every assumption before issuing drawings. This keeps the estimate traceable. This improves review confidence.
FAQs
What is a commercial lighting load?
It is the estimated electrical demand for general lighting. It helps size panels, feeders, and branch circuits during commercial electrical planning.
What does VA per square foot mean?
It means volt-amperes assigned to each square foot. The value is multiplied by calculated floor area to estimate lighting demand.
Should I use the area method or fixture method?
Use the area method during early design. Use the fixture method after lighting schedules are available. The higher option gives conservative planning.
Why does the calculator include power factor?
Power factor converts fixture watts into volt-amperes. Lower power factor increases apparent load and can affect current calculations.
What is driver or ballast loss?
It is extra input power used by lighting drivers or ballasts. Add this percentage when fixture wattage excludes those losses.
When should continuous load be selected?
Select it when lighting may operate for long periods. Many commercial spaces treat general lighting as continuous for planning.
Why add spare capacity?
Spare capacity supports future fixture changes, tenant revisions, and added lighting zones. It also reduces redesign risk later.
How are branch circuits estimated?
The calculator divides final load by usable circuit capacity. It rounds upward because partial circuits still need full circuit allocation.
Can this replace an engineer?
No. It is a planning tool. A qualified professional must confirm code rules, drawings, equipment ratings, and project assumptions.
Does voltage change the total load?
Voltage does not change volt-amperes. It changes current, circuit capacity, and the likely number of branch circuits.
Can I export the result?
Yes. Use the CSV button for spreadsheet review. Use the PDF button for a simple project record.