Construction Service Load Calculator
Enter connected loads, demand assumptions, motor allowance, reserve, phase, voltage, and power factor.
Formula Used
General load = Area × (Lighting VA per sq ft + Receptacle VA per sq ft)
Base load = General load + appliance loads + laundry loads + fixed equipment + kitchen equipment + lift load + welder load + process load + water heater + pump + noncontinuous load
Demanded base = Base load × Demand factor
Selected HVAC = Greater of cooling load or heating load
Adjusted continuous load = Continuous load × 1.25
Adjusted motor load = Largest motor load × 1.25
Raw service load = Demanded base + Selected HVAC + Adjusted continuous load + Adjusted motor load
Final service load = Raw service load + Future spare allowance + Safety allowance
Single phase amps = Final VA ÷ (Voltage × Power factor)
Three phase amps = Final VA ÷ (1.732 × Voltage × Power factor)
This calculator supports planning estimates. Local codes, utility rules, and professional design review still apply.
How to Use This Calculator
- Enter the building area and area based lighting or receptacle allowances.
- Add appliance circuits, fixed equipment, kitchen loads, shop loads, pumps, and water heating.
- Enter heating and cooling loads. The calculator uses the larger value.
- Add the largest motor, continuous loads, and noncontinuous loads.
- Set demand factor, future spare, safety margin, voltage, power factor, and phase type.
- Press the calculate button. The result appears above the form.
- Use the CSV button for spreadsheet records. Use the PDF button for printing.
Example Data Table
| Input | Example Value | Meaning |
|---|---|---|
| Area | 4,000 sq ft | Used for area based load. |
| Lighting and receptacles | 3 and 1.5 VA/sq ft | Creates 18,000 VA general load. |
| Appliance and laundry | 4,500 VA | Added as circuit based load. |
| Fixed, kitchen, water, pump, other | 22,500 VA | Added before demand factor. |
| Demand factor | 75% | Base load becomes 33,750 VA. |
| Selected HVAC | 18,000 VA | Cooling is larger than heating. |
| Motor and continuous allowance | 11,875 VA | Both are adjusted at 125%. |
| Final result | 73.49 kVA, 306.20 A | Rounded suggested service is 400 A. |
Service Load Planning for Construction
Service load planning starts before panels are ordered. It helps a builder size feeders, main breakers, temporary boards, and final service gear. A good estimate includes lighting, receptacles, motors, fixed equipment, heating, cooling, and future spare capacity. It also separates continuous loads from short use loads. That distinction matters because continuous loads stay energized for long periods. They need extra allowance.
What the Calculator Reviews
This calculator treats the project as a coordinated load schedule. Floor area creates a base lighting and receptacle allowance. Small appliance and laundry circuits add known volt amp values. Fixed equipment, kitchen equipment, pumps, elevators, welders, and process tools add direct loads. Heating and cooling are compared, then the larger value is used. Most buildings do not use full heating and full cooling at the same time.
Demand and Motor Adjustments
A demand factor reduces selected connected loads when all items are unlikely to run together. The factor should match the design rule, engineer direction, or local practice used on the job. The largest motor receives an added allowance. Motors can draw higher current while starting. A stronger service estimate should show that extra load clearly.
Continuous Load and Reserve
Continuous loads are multiplied by 125 percent in this calculator. That makes the result more conservative for lighting banks, controls, signs, and equipment that may stay on for hours. Future spare capacity is also useful. It covers tenant changes, added tools, or later mechanical upgrades. A safety margin can then be added for planning comfort.
Reading the Final Output
The final service load is shown in volt amps and kilovolt amps. The current is calculated from the voltage, phase type, and power factor. Single phase and three phase systems use different current formulas. The recommended service size is rounded up to a common amp rating. This does not replace code review. It gives an organized planning estimate for early budgeting, coordination, and field checking.
Coordination Tips
Use this number with panel schedules, utility notes, and equipment submittals. Check nameplates before final issue. Ask the authority having jurisdiction about required methods. Document assumptions in the estimate. Keep spare capacity visible, not hidden inside rounded inputs. Clear notes help trades compare revisions and avoid costly service changes later. Recheck before procurement starts.
FAQs
What is a service load calculation?
It estimates the electrical load that a building service must carry. It combines lighting, receptacles, fixed equipment, motors, heating, cooling, and allowances. The result helps size service equipment during planning.
Is this calculator a final code design?
No. It is a planning tool. Final service sizing should be checked against local electrical rules, utility requirements, equipment nameplates, and a licensed professional’s review.
Why is the larger HVAC value used?
Heating and cooling often do not run at full load together. The calculator compares both values and uses the larger one for the service estimate.
What does demand factor mean?
Demand factor reduces selected connected loads when all loads are unlikely to operate at once. Use a value approved by your design method or project authority.
Why are continuous loads multiplied by 125 percent?
Continuous loads may operate for long periods. The 125 percent allowance creates extra capacity for loads that stay on and keeps the estimate conservative.
How is three phase current calculated?
Three phase current is calculated from volt amps divided by square root of three, voltage, and power factor. This gives line current for balanced planning.
What is the largest motor allowance?
The largest motor field adds a 125 percent motor contribution. It allows extra service capacity for motor starting and heavy motor operation.
Can I include future expansion?
Yes. Enter a future spare percentage. The calculator adds that reserve after the main service load is calculated.
What power factor should I use?
Use the known project value when available. If unknown, use 1.00 for a simple estimate, or a lower value when motors and inductive equipment dominate.
Why does the recommended service size round up?
Service equipment comes in common amp ratings. The calculator rounds the calculated current up to the next listed planning size.
Can this help with construction bidding?
Yes. It can support early pricing, scope checks, and coordination. It should be updated when equipment schedules and drawings become final.