Electrical Load Calculator

Commercial Electrical Load Calculator — Free Tool

Optional. Used to check available panel capacity.

Equipment / Load Description Load Type Watts Each Qty Total Watts

Load Calculation Results

—
Total Watts
—
Total kW
—
Total Amps Drawn
—
Min Breaker (NEC 80%)
—
Min Wire Gauge
Talk to an FSG Electrician →

Optional. Leave blank to see available capacity only. Use our Watts to Amps Calculator to convert wattage to amps.

Panel Capacity Results

—
Panel Capacity (A)
—
Estimated In Use (A)
—
Available (A)
—
Available (kW)
Talk to an FSG Electrician →

What This Electrical Load Calculator Does

This free tool helps facility managers, property owners, and electrical contractors estimate circuit and panel loads for commercial buildings. Unlike residential load calculators that focus on home appliances and service entrance sizing, this calculator is built around the real commercial use cases FSG's team handles every day: adding EV chargers to a warehouse, retrofitting LED lighting across a large facility, installing new HVAC equipment in a tenant space, or checking whether an existing panel has room for new loads before calling an electrician.

Mode 1 (Add-a-Load Checker) lets you build a list of equipment, calculates total amps drawn, and applies the NEC 80% continuous load rule to recommend a minimum breaker size and wire gauge. Mode 2 (Panel Capacity Checker) lets you enter your existing panel size and estimated current load to see how much capacity you have left before a panel upgrade becomes necessary.

For the underlying amp conversion math, see our Watts to Amps Calculator. For EV charger installation at your facility, see FSG's commercial EV charging services.

The Formulas This Calculator Uses

Single Phase Load

Amps = Watts / Volts Example (120V, 1,000W): 1,000 / 120 = 8.33A NEC 80% breaker: 8.33 / 0.8 = 10.4A Next standard: 15A

Three Phase Load

Amps = Watts / (V x 1.732) Example (208V 3ph, 10,000W): 10,000 / (208 x 1.732) = 10,000 / 360.3 = 27.8A NEC 80% breaker: 27.8 / 0.8 = 34.7A Next standard: 40A

NEC 80% Rule

Continuous loads must not exceed 80% of breaker rating (NEC 210.19, 210.20). Breaker min = Amps / 0.8 Wire must match or exceed the breaker rating per NEC 310 ampacity tables.

Common Commercial Equipment Load Reference

Use these typical wattage values when building your load list. Actual values vary by manufacturer and model. Always verify against the equipment nameplate for permitted work.

Equipment Type Typical Wattage Voltage / Phase Load Type Notes
LED Troffer (2x4)40-50W120V or 277V, 1phContinuousMost common commercial office fixture
LED High Bay (100W)100W120/277V, 1phContinuousWarehouse and industrial ceiling lights
LED High Bay (200W)200W277/480V, 1phContinuousHigh-ceiling distribution centers
Rooftop HVAC (5 ton)5,000-6,000W208/240V, 3phContinuousTypical small commercial unit
Rooftop HVAC (10 ton)10,000-12,000W208/480V, 3phContinuousMid-size commercial unit
EV Charger Level 2 (EVSE)7,200W (30A)208/240V, 1phContinuousNEC requires 125% sizing for EVSE
EV Fast Charger (DC)50,000W+480V, 3phContinuousRequires load study for most facilities
Air Compressor (5 HP)3,730W208/240V, 3phNon-continuousMotor load, typically cyclic
Air Compressor (10 HP)7,460W208/480V, 3phNon-continuousMotor load, typically cyclic
Commercial Refrigeration1,500-3,000W208/240V, 1phNon-continuousCycles on and off
Office Workstation (avg)300-400W120V, 1phNon-continuousPer NEC 220.14, use 180VA minimum per receptacle
Server / IT Rack3,000-10,000W208V, 1ph or 3phContinuousVerify nameplate; treat as continuous
Planning an EV charger installation? Each Level 2 EVSE is treated as a continuous load under NEC 625.42, requiring the circuit to be sized at 125% of the charger's rated amperage. A fleet of 10 chargers at 30A each needs a 375A minimum circuit capacity. FSG's EV charging team handles load studies, panel upgrades, and installation across all facility types.

Commercial Electrical Load Calculation Example

A worked example: a facility manager at a 50,000 sq ft distribution center wants to add 8 Level 2 EV chargers (7,200W each) on a 208V three-phase panel currently rated at 400A and estimated 60% loaded.

Step 1 — Total New Load Wattage

  • 8 chargers x 7,200W = 57,600W total
  • EV chargers are continuous loads (NEC 625.42)

Step 2 — Convert to Amps (Three Phase)

  • Amps = 57,600 / (208 x 1.732) = 57,600 / 360.3 = 159.9A
  • NEC 80% continuous load rule: 159.9 / 0.8 = 199.9A minimum breaker
  • Next standard size: 200A breaker required

Step 3 — Check Panel Capacity

  • 400A panel at 60% loaded = 240A already in use
  • Available: 400A - 240A = 160A remaining
  • New load requires 200A. Panel is 40A short.
  • Verdict: Panel upgrade required before installation

Standard Commercial Panel Sizes and Ampacity

Panel Size NEC 80% Continuous Limit Typical Application Common Voltage
100A80A continuousSmall tenant suites, single-zone retail120/240V 1ph
200A160A continuousMid-size offices, restaurants, small retail120/208V 3ph
400A320A continuousLarge offices, warehouses, distribution120/208V or 277/480V 3ph
600A480A continuousLarge retail, multi-tenant commercial277/480V 3ph
800A640A continuousIndustrial facilities, data centers277/480V 3ph
1,200A960A continuousLarge manufacturing, campus feeders277/480V 3ph

Frequently Asked Questions

The NEC 80% rule (Sections 210.19 and 210.20) requires that any circuit serving a continuous load -- defined as a load expected to operate for three or more hours -- must be sized so the load does not exceed 80% of the circuit breaker's ampere rating. For example, if your continuous load draws 80 amps, your breaker must be rated at least 100A. This rule exists because breakers can overheat when operated at 100% of their rating for extended periods. This calculator applies the 80% rule automatically to all load calculations and breaker recommendations.
The best way to check panel capacity is a load calculation performed by a licensed electrician using a clamp meter to measure actual loads on each circuit. As a planning estimate, you can use Mode 2 of this calculator: enter your panel size and a rough estimate of current loading. Most commercial panels run between 60% and 80% loaded. If the new load you want to add pushes your total over 80% of panel capacity, a panel upgrade or a separate sub-panel feed is likely required. FSG's electricians can perform an on-site load study to give you exact numbers before any equipment purchase.
Single phase power uses two conductors (hot and neutral) and is common for lighting, receptacles, and smaller equipment. Three phase power uses three hot conductors and delivers power more efficiently for larger loads -- motors, HVAC systems, EV chargers, and industrial equipment all commonly use three phase. In a three phase system, the same wattage of load requires fewer amps than single phase, which is why three phase is standard in commercial and industrial facilities. The amperage formula differs: single phase uses Amps = Watts / Volts, while three phase uses Amps = Watts / (Volts x 1.732).
It depends on your existing panel capacity and current load. Each Level 2 EV charger (typically 7,200W at 30A on a 240V circuit) is treated as a continuous load under NEC 625.42, meaning the circuit must be sized at 125% of the charger's rated amperage. A fleet of chargers adds up quickly -- 10 chargers at 30A each require around 375A of new circuit capacity at minimum. Many commercial facilities need a panel upgrade, a new sub-panel, or load management equipment before fleet EV charging is feasible. FSG's EV charging team handles the full scope from load study through installation.
This calculator provides planning-level estimates based on NEC formulas and is useful for early budgeting, feasibility checks, and scoping conversations before calling an electrician. It does not replace a full NEC 220 load calculation required for permitted work, which accounts for demand factors, motor starting loads, specific equipment nameplate data, and local utility requirements. For any project that involves panel modifications, new service, or permitted electrical work, FSG's licensed electricians can provide a code-compliant load study and design.
This calculator supports all five standard commercial voltages: 120V single phase (receptacles, small lighting), 208V three phase (commercial standard in most office and retail buildings), 240V single phase (HVAC, larger single-phase equipment), 277V single phase (the most common voltage for commercial fluorescent and LED lighting in 480V systems), and 480V three phase (motors, large HVAC, industrial equipment, and DC fast chargers). If you are unsure which voltage applies, check the equipment nameplate or the panel label. FSG's Watts to Amps Calculator uses the same voltage options for circuit-level conversions.

Need a panel evaluation or load study?

FSG's licensed commercial electricians perform on-site load studies, panel upgrades, and electrical infrastructure work for facilities of any size -- nationwide. Get real numbers before you invest in new equipment.

Talk to an Electrician EV Charging Services
Disclaimer: Results are planning-level estimates based on NEC formulas and are intended for early feasibility and scoping purposes only. Actual load calculations for permitted work must be performed by a licensed electrical engineer or contractor using NEC Section 220 methods, equipment nameplate data, and local utility requirements. Always consult a licensed electrician before modifying any commercial electrical system.