Electrical Panel Sizing Guide: How Many Amps Do You Need?

Standard Electrical Panel Sizes

Residential electrical panels (also called load centers or breaker boxes) come in standard sizes measured in amps. The panel size determines the total electrical capacity of your home:

60 amp: Very old homes from the 1940s–1960s. Inadequate for modern usage. Replace immediately.
100 amp: Common in homes built before 1990. Adequate for modest homes without EV chargers, hot tubs, or electric dryers. Borderline for modern loads.
150 amp: Mid-range panel found in some 1980s–1990s construction. Adequate for most average homes.
200 amp: The modern standard for new construction. Provides 48,000 watts of capacity (200A × 240V). Supports most typical home loads comfortably.
400 amp: Required for very large homes, multiple EV chargers, or homes with all-electric HVAC and appliances. Often installed as two 200A panels.

How to Calculate Your Electrical Load

To determine if your panel has adequate capacity, add up the amperage of your major electrical loads. This is called a load calculation:

List all 240V appliances: central A/C (typically 30–50A), electric range (40–50A), electric dryer (30A), electric water heater (30A), EV charger (32–48A), hot tub (50A)
Estimate general lighting and receptacle load (typically 3 watts per sq ft of living space)
Add all loads together and multiply by 1.25 (NEC safety factor)
Compare to panel capacity

Example: A/C (40A) + range (45A) + dryer (30A) + water heater (30A) + general load (50A equivalent) = 195A × 1.25 = 244A. A 200A panel handles this — the NEC demand factor calculation reduces coincident loads, but a 200A service is the minimum.

When to Upgrade Your Electrical Panel

Consider upgrading your panel when:

You're adding an EV charger (Level 2 chargers require 32–48 amps on a dedicated circuit)
Installing a hot tub, pool, or sauna
Adding central air conditioning to a home that previously had window units
Building an addition that adds significant square footage
Converting from gas to electric appliances (heat pump, electric range, electric dryer)
Circuit breakers trip regularly under normal loads
You have a Federal Pacific Stab-Lok or Zinsco panel (these have documented safety issues and should be replaced regardless of capacity)

Cost to Upgrade Your Electrical Panel

100A to 200A upgrade: $1,500–$4,000 including labor, new panel, permits
200A to 400A upgrade: $3,500–$8,000 (may require utility service upgrade)
Full service entrance replacement: $2,000–$5,000 if the utility-side service entrance also needs updating

All panel upgrades require a permit and inspection. Permit fees typically run $100–$500. This is not a DIY project — panel work must be performed by a licensed electrician in all jurisdictions.

Smart Panels

New smart panels from companies like Span, Leviton, and Siemens allow circuit-level monitoring and control via smartphone app. They cost $1,500–$3,000 more than standard panels but provide detailed energy monitoring, automatic load management (to prevent tripping the main breaker), and integration with home batteries and EV chargers. Worth considering if upgrading for EV or solar+battery storage.

Frequently Asked Questions

Do I need to upgrade to 200 amp service?

If you have a 100-amp panel and plan to add an EV charger, new HVAC system, hot tub, or major kitchen appliance, upgrading to 200 amps is strongly recommended. A 100-amp service limits your options and may become a constraint for future home improvements. 200A is the standard for all new construction for good reason — the incremental cost to upgrade now is much less than the disruption of upgrading later.

How do I know if my panel is full?

A panel is 'full' when all breaker slots are occupied and there's no room to add new circuits. Tandem (slim) breakers can sometimes add capacity in a full panel, but this depends on the panel manufacturer's specifications. If you need new circuits but your panel is full, you can add a subpanel or upgrade the main panel. Check your panel door — it typically shows which slots accept tandem breakers.

What's the cost to upgrade an electrical panel?

Upgrading from 100A to 200A typically costs $1,500–$4,000 all-in, including the new panel, labor, permits, and inspection. If the utility service entrance (the wires from the street) also needs upgrading, add another $1,000–$2,500. Costs vary by region — urban areas with higher labor costs tend toward the top of the range.

Can I add a subpanel instead of upgrading the main panel?

Yes — adding a subpanel is a good option when you need additional circuits in a specific location (garage, workshop, addition) without upgrading the entire service. A subpanel is fed from the main panel and distributes power to the new area. However, if your main panel itself is already at or near capacity (100A service with heavy loads), a subpanel alone won't solve the underlying capacity problem.

How many circuits does a 200 amp panel support?

A 200-amp panel typically has 40–42 circuit slots, supporting 20–40 individual circuits (some slots can use tandem/slim breakers to double capacity). Standard homes need 20–30 circuits. Each major appliance gets a dedicated circuit; general areas share circuits at 15A or 20A. The panel's amperage rating represents total capacity, not the number of circuits.