How do I calculate my electrical panel load?

Per NEC Article 220, add all circuit loads, apply demand factors (100% for first 10 kVA of general lighting, 40% for remainder), then add HVAC and appliances. The result in amps at 240V is your calculated load. Your service must be rated at least 25% above this value.

What size electrical service do I need?

Most modern homes need 200-amp service. Homes with electric HVAC, EV charger, electric range, and multiple large appliances may need 400A. Add up all major loads, apply NEC 220 demand factors, and the calculated load in amps drives the service size selection (100A/150A/200A/400A).

What is the NEC demand factor for general lighting?

NEC Table 220.42: First 3,000 VA at 100%. Next 3,001 to 120,000 VA at 35%. Remainder above 120,000 VA at 25%. This demand factor applies to general-use branch circuit loads (lighting + receptacles at 3 VA/sq ft).

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Electrical Panel Load Calculator

NEC Article 220 demand load calculation — service sizing and capacity analysis

0A Calculated load

200A Service needed

0A Spare capacity

0% Panel utilization

Home Basics

Conditioned floor area

sq ft

Used for general lighting load (3 VA/sq ft per NEC 220.12)

Small appliance circuits

1,500 VA each per NEC 220.52

Laundry circuits

1,500 VA each per NEC 220.52(B)

Major Appliances

Electric range / oven

Electric dryer

Electric water heater

HVAC

Air conditioning

Electric heat / heat pump backup

Other Loads

EV charger

Other fixed loads

Pool pump, spa, workshop, etc.

Demand Load Summary

0 amps calculated load

Recommended service

200A

Load Distribution

NEC 220 Calculated Load Schedule

Load item	Connected VA	Demand factor	Demand VA

Per NEC Article 220 Standard Method. Heating vs. cooling — only the larger load is used (NEC 220.60).

When to Upgrade Your Panel

⚠ Consider upgrade

Panel utilization above 80%
No breaker spaces available
Frequently tripping breakers
Adding EV charger to 100A service
Converting from gas to all-electric

🚨 Upgrade required

Calculated load exceeds service rating
Federal Pacific or Zinsco panel
Fuse box (pre-breaker era)
Aluminum branch wiring (pre-1972)
Panel over 40 years old

Upgrade Cost Ranges (2025)

Upgrade type	Typical cost
100A → 200A service upgrade	$1,200–$3,000
200A panel replacement	$1,500–$4,000
200A → 400A service upgrade	$3,000–$8,000
Add subpanel (100A)	$500–$1,500
Load management device	$200–$600

Service Size Decision Guide

Service	Homes suited for	Max calc. load
100A	Small home, gas HVAC, no EV	80A (80%)
150A	Medium home, mixed fuels	120A (80%)
200A	Standard home, 1 EV, central AC	160A (80%)
400A	All-electric, 2+ EVs, large home	320A (80%)

Load Management Options

Smart load management devices can defer non-critical loads (EV charging, water heater, HVAC) when demand spikes, allowing a 200A panel to support loads that would otherwise need 400A service. Products like Span, Lumin, and EnergyHub panels offer this capability. Particularly useful for adding EV charging to an existing 150–200A panel.

NEC Article 220 Key Sections

Section	Description
220.12	Lighting load — 3 VA per sq ft for dwellings
220.42	Demand factors for lighting loads
220.52(A)	Small appliance circuits — 1,500 VA each, min 2 circuits
220.52(B)	Laundry circuits — 1,500 VA each
220.54	Electric dryers — use nameplate or 5,000 W min
220.55	Household cooking appliances — demand factor table
220.60	Noncoincident loads — use largest only (heat vs. AC)
220.61	Neutral load calculation — can reduce neutral conductor
230.79	Rating of service disconnecting means

NEC Table 220.42 — Lighting Demand Factors

Portion of load	Demand factor
First 3,000 VA	100%
3,001–120,000 VA	35%
Over 120,000 VA	25%

NEC Table 220.55 — Range Demand Factors

Number of ranges	Max kW demand
1 range, up to 12 kW	8 kW
1 range, 12.1–27 kW	kW rating (no factor)
2 ranges	11 kW
3–4 ranges	14 kW

How to Use This Calculator

List all your circuits

Identify every branch circuit in your panel — lighting, receptacles, appliances, HVAC, and dedicated circuits. You can find these on your panel door or from a home inspection report.

Enter amperage per circuit

For each circuit, enter the breaker amperage (15A, 20A, 30A, 40A, 50A, etc.). For 240V circuits, enter both poles. Use the general lighting load (sq ft × 3 VA) for unlisted circuits.

Note 120V vs 240V loads

Double-pole breakers (240V) count on both bus bars. Single-pole (120V) count on only one side. Balancing loads across both hot bus bars is important for efficient service use.

Check total vs panel capacity

Compare your calculated load total to your service size (100A, 150A, 200A). The NEC 80% rule limits continuous loads to 80% of service rating.

Review demand factor

NEC Article 220 demand factors allow you to derate certain loads (lighting, general receptacles) since not all circuits run at full capacity simultaneously.

Key Terms

Demand Factor — A ratio applied to calculated loads to reflect that not all circuits operate at full power simultaneously. NEC 220.42 allows reducing lighting loads above 3,000 VA to 35% for service sizing.

Main Breaker — The primary overcurrent device at the top of the panel that protects all circuits and the service entrance conductors. Rated to match the service size (100A, 200A, etc.).

Service Entrance — The conductors from the utility meter to the main panel. Sized for the total calculated load after applying demand factors per NEC Article 220.

Load Center — Another term for the main electrical panel or breaker box. Contains the main breaker, bus bars, and all branch circuit breakers.

Balanced Load — Distributing single-phase 120V circuits equally across both hot bus bars (A and B legs) so neither leg is significantly more loaded. Unbalanced loads reduce efficiency and can cause neutral conductor overheating.

NEC 220 — National Electrical Code Article 220 covering branch circuit, feeder, and service load calculations. Provides the methodology and demand factors for sizing electrical service.

Frequently Asked Questions

What is a demand factor and why does it matter?

A demand factor recognizes that not all loads run simultaneously at full power. NEC 220.42 allows you to calculate only 35% of lighting loads above 3,000 VA, and NEC 220.60 lets you omit either heating or cooling (whichever is smaller). Without demand factors, nearly every home would appear to need 400A service.

Can I add a subpanel instead of upgrading service?

Yes — if your service has capacity but your main panel lacks breaker spaces. A subpanel fed from the main panel can add circuits without a utility service upgrade. However, if your calculated load exceeds the service rating, you'll need both a new panel and a service upgrade from the utility company.

Does a 200-amp panel mean I can use 200 amps continuously?

NEC 210.20 limits continuous loads to 80% of breaker rating. For a 200A main breaker, the safe continuous load is 160A. Momentary peaks above 160A are fine, but if your average demand consistently exceeds 160A, you need larger service.

How does NEC 220.60 handle heating and cooling?

NEC 220.60 allows you to omit the smaller of heating or cooling loads when calculating total demand, since both cannot run at the same time. You include only the larger. If your heat pump uses both compressor and strip heat simultaneously (defrost mode), include the combined heating load — not just the strip heat.

What happens if my calculated load exceeds my service?

You'll need a service upgrade — a new meter base, service entrance conductors, and a new main panel rated for the larger amperage. This requires a utility company disconnect, permit, inspection, and reconnect. Plan for $2,000–$5,000 for a 200A upgrade, or $4,000–$10,000 for 400A depending on location.