Load Center Calculator

Size a residential or commercial load center with the NEC Article 220 standard method — general lighting and appliance demand factors, range/dryer sizing, HVAC and largest-motor adders, and a three-phase or split-phase panel balance check, all in one tool. Residential mode follows the dwelling-unit method (NEC 220.42, 220.52–220.55); Commercial mode uses occupancy-based lighting loads across thirteen occupancy types (NEC Table 220.12), general-use receptacles, and — for restaurants — kitchen-equipment demand factors (NEC Table 220.56). Both modes let you reserve spare breaker spaces for future circuits and work together with the phase/leg balance section to check load distribution across L1/L2 or A/B/C. Results include a standard-size utilization chart, a phase/leg balance chart, and a print view that captures both exactly as they appear on screen. Built for electricians, electrical engineers, facility managers, and students studying for licensing exams.

Choose Residential or Commercial, select the voltage system, enter the load details, and click Calculate. Both modes work standalone or together with the phase/leg balance section below.

Voltage System

ℹ️ 277/480V is atypical for dwelling-unit branch circuits — NEC 210.6 caps standard residential receptacle/lighting circuits at 120/240V nominal, with 208Y/120 used in some multi-family services. Verify this voltage system with your AHJ before applying it to a dwelling-unit calculation.

Quick Presets

Dwelling & Circuits

Dwelling Square Footage (3 VA/ft² general lighting)

Small-Appliance Circuits (min. 2, NEC 220.52(A))

Laundry Circuits (min. 1, NEC 220.52(B))

Fixed Appliances (4+ gets 75% demand factor, NEC 220.53)

Range, Dryer & HVAC

Range Nameplate (kW, NEC Table 220.55)

Dryer Nameplate (kW, min. 5, NEC 220.54)

Heating Load (kW, larger of heat/cool counted)

Cooling Load (kW, 125% continuous applied)

Largest Motor Load (VA — 25% adder, NEC 430.24)

Spare Spaces (future circuits, +10A each)

Building & Occupancy

Building Square Footage

Occupancy Type (NEC Table 220.12 VA/ft²)

General-Use Receptacles (count, 180 VA each, NEC 220.14(I))

HVAC, Kitchen & Motors

Heating Load (kW, larger of heat/cool counted)

Cooling Load (kW, 125% continuous applied)

Kitchen Equipment Units (count, NEC Table 220.56)

Kitchen Equipment Load (total connected kVA)

Largest Motor Load (VA — 25% adder, NEC 430.24)

Other Connected Load (VA, optional catch-all)

Spare Spaces (future circuits, +10A each)

Results

Recommended Load Center

—

Total Demand Load

—

kVA

Required Amps

—

Spare Capacity

—

Panel Utilization—

Formula: —

Standard Load Center Sizes — Utilization

Each bar is a standard load-center rating, and the height is how much of that rating the demand plus spare space uses. The size this page recommends is marked in gold. The dashed line is 100 percent of the rating.

Neighboring Sizes Recommended Size 100% Capacity

⚖️ Phase / Leg Balance

Add individual circuits below and assign each to a leg or phase — this works together with the mode above using the same voltage system selection. Runs automatically as part of Calculate.

Add circuits above, then click Calculate, to see leg/phase balance.

🔌 Once you know the recommended load center size, verify individual branch-circuit breaker sizing with the Circuit Breaker Sizing Calculator.

🔺 Sizing a genuinely balanced three-phase feeder or service, not just checking an existing load list? The Three Phase Power Calculator covers the full power/current relationship in more depth.

Results are engineering estimates based on published NEC Article 220 formulas and demand-factor tables (220.12, 220.42, 220.52, 220.53, 220.54, 220.55, 220.56, 220.60, 220.14(I)) and NEC 430.24. Several simplifications are disclosed in the Comprehensive Guide below. The panel size still has to be checked against the installation and the adopted edition of the National Electrical Code (NFPA 70). Verify with a licensed electrician before any electrical work.

How to Use the Load Center Calculator

Choose Residential or Commercial

Pick Residential for a dwelling-unit service sized by the NEC 220 Part III standard method, or Commercial for an occupancy-based method.

Select the Voltage System

Choose 120/240V single-phase, 120/208Y three-phase, or 277/480Y three-phase. This also drives the phase/leg balance analysis below.

Enter the Load Details

Enter square footage, fixed appliances, range/dryer, HVAC, and largest-motor load for Residential; or square footage, occupancy, receptacles, HVAC, kitchen equipment, and motor load for Commercial. Or tap a Quick Preset.

Calculate, Review Balance, and Print

Click Calculate to see the recommended load center size, total demand load, and utilization. Optionally add circuits to the Phase/Leg Balance section — it works together with the mode above automatically. Use Print to capture results and both charts exactly as they appear on screen.

Comprehensive Guide to Load Center Sizing

The NEC 220 Part III standard method (Residential)

General lighting load is calculated at 3 VA per square foot (NEC Table 220.12), plus at least two 1,500 VA small-appliance circuits (NEC 220.52(A)) and at least one 1,500 VA laundry circuit (NEC 220.52(B)). That subtotal is demand-factored per NEC Table 220.42: the first 3,000 VA at 100%, the next up to 120,000 VA at 35%, and any remainder at 25% — reflecting that a dwelling rarely runs every circuit simultaneously at full load.

Fixed appliances and the 75% rule

NEC 220.53 permits a 75% demand factor when four or more fixed appliances (other than range, dryer, space-conditioning equipment, or laundry) are on the same feeder or service. Fewer than four appliances are counted at 100%. This calculator applies that threshold automatically based on how many appliances you've added to the list.

Range and dryer sizing (single-appliance case)

NEC Table 220.55, Column C, sets an 8 kW demand for a single range rated up to 12 kW, increasing 5% per kW (or major fraction) above 12 kW, up to 27 kW. NEC 220.54 sets dryer demand at 100% of nameplate rating, with a 5 kW minimum for a single dryer. Multiple ranges or dryers on one service use different table columns and are not modeled here.

HVAC and noncoincident loads

NEC 220.60 permits counting only the larger of heating or cooling load when the two are noncoincident — a home or building rarely runs full heating and full cooling at the same time. This calculator takes the larger of your entered heating/cooling values and applies a 125% continuous-duty factor (NEC 210.20(A)), since HVAC equipment commonly runs three hours or more continuously.

The largest-motor 25% adder

NEC 430.24 requires feeder conductors supplying multiple motors to be sized for the sum of all motor full-load currents, plus 25% of the largest motor's full-load current — because the largest motor's starting (inrush) current adds meaningfully to peak demand even though it's brief. Enter your largest single motor's connected VA and this calculator adds that 25% on top of the total demand.

Commercial occupancy-based method

Commercial mode starts from NEC Table 220.12's published VA/ft² figures by occupancy type, applied at 100% of connected value — a deliberately conservative simplification rather than modeling every occupancy-specific demand-factor row of NEC Table 220.42, consistent with how several comparable commercial load tools in the market handle this. General-use receptacles not already covered by a unit lighting load are added at 180 VA each per NEC 220.14(I).

Kitchen equipment demand (restaurant occupancy)

NEC Table 220.56 permits a demand factor based on the number of pieces of kitchen equipment on a feeder: 100% for two or fewer units, stepping down to 65% for six or more. This calculator applies that published step table to your entered kitchen equipment count and total connected kVA when Restaurant occupancy is selected.

Spare space / future-expansion allowance

Since the load for an anticipated future circuit is undetermined at design time, a common planning practice is to add roughly 10A of headroom per reserved breaker space before selecting a standard load-center size. This calculator lets you set that count directly (default 2) and adds the headroom before rounding up.

Phase / leg balance (working together with either mode)

On a 120/240V split-phase service, loads should be distributed as evenly as practical between L1 and L2; on a three-phase service, across A, B, and C. Meaningful imbalance increases neutral conductor current and can strand usable capacity on the lighter leg or phase. This calculator's balance section reads whichever mode (Residential or Commercial) and voltage system is active, letting you add individual circuits and see the resulting distribution — a planning-level estimate, not a certified neutral-conductor calculation.

Worked Examples

Four real-world scenarios. Click "Load This Example" to run it in the calculator above.

1. Residential — 2,400 ft² Single-Family Home, 120/240V

A 2,400 ft² home with a 12kW range, 5kW dryer, 4kW AC, and four fixed appliances totaling 8,100 VA. Four spare spaces reserved for future circuits.

Total demand ≈ 30.1 kVA → 125.5A + 40A spare = 165.5A required → 200A load center recommended (≈83% utilization).

2. Residential — 950 ft² Apartment Unit, 120/208Y/120V (Multi-Family)

A small apartment unit fed from a 3-phase building service, with an 8kW range, 5kW dryer, and 3.5kW AC.

Total demand ≈ 21.9 kVA → 60.8A + 20A spare = 80.8A required → 100A load center recommended (≈81% utilization).

3. Commercial — 5,000 ft² Office Building, 120/208Y/120V

An office building with 20 general-use receptacles, 18kW cooling load, and a 2,000 VA largest motor (elevator or pump).

Total demand ≈ 47.1 kVA → 130.8A + 40A spare = 170.8A required → 200A load center recommended (≈85% utilization).

4. Commercial — Restaurant Kitchen, 120/208Y/120V (with Phase Balance)

A 2,200 ft² restaurant with 5 kitchen equipment units totaling 45 kVA connected, plus walk-in cooler, hood fan, griddle, and lighting circuits assigned across phases A/B/C.

Total demand ≈ 56.4 kVA → 156.4A + 30A spare = 186.4A required → 200A load center recommended (≈93% utilization — near the 80% planning threshold).

Standard Load Center Sizes — Reference

Common standard load-center/panel ratings and typical use case, for orientation — not a substitute for the calculated result above.

Standard Size	Typical Use

Frequently Asked Questions

How does this calculator size a residential load center?

Residential mode follows the NEC 220 Part III standard method: general lighting load (3 VA/ft²), small-appliance and laundry circuits, and fixed appliances are summed and demand-factored per NEC Table 220.42, then a range (NEC 220.55), dryer (NEC 220.54), HVAC at 125% continuous duty, and a 25% largest-motor adder (NEC 430.24) are added. The total demand load is converted to amps and rounded up to a standard load-center size.

What's the difference between Residential and Commercial mode?

Residential mode uses the dwelling-unit demand-factor method described above. Commercial mode uses an occupancy-based general lighting load (NEC Table 220.12 VA/ft² by occupancy type), general-use receptacles at 180 VA each (NEC 220.14(I)), the same HVAC and motor treatment, and — for restaurant occupancy — a kitchen-equipment demand factor from NEC Table 220.56.

How is the range/dryer demand calculated?

This tool models a single range and single dryer per NEC Table 220.55 Column C and NEC 220.54: a range up to 12 kW carries an 8 kW demand, increasing 5% per kW (or major fraction) above 12 kW up to 27 kW; a dryer is demanded at 100% of nameplate, with a 5 kW minimum. Multiple ranges or dryers on one service are not modeled — use the full NEC Table 220.55 Column A/B for that case.

What does the largest-motor 25% adder mean?

NEC 430.24 requires branch-circuit and feeder conductors supplying multiple motors to be sized for the sum of all motor full-load currents plus 25% of the largest motor's current. This calculator applies that same principle at the load-center level: enter the largest single motor's connected VA, and 25% of it is added on top of the total demand load.

What is phase/leg balance and why does it matter?

Phase/leg balance checks how evenly individual circuit loads are distributed across a panel's two legs (120/240V split-phase) or three phases (208Y or 480Y three-phase). Significant imbalance increases neutral conductor current and can waste panel capacity on the heavier leg or phase. This calculator's balance section is a planning-level estimate — actual neutral current also depends on load type (linear vs. harmonic-producing), which isn't modeled here.

Can I use a three-phase voltage system for a residential service?

Yes — this calculator offers 120/208Y/120V and 277/480Y/277V under Residential mode as well as Commercial, since multi-family and apartment buildings are sometimes fed from a three-phase service. Note that NEC 210.6 caps standard dwelling-unit branch-circuit voltage at 120/240V nominal, with 208Y/120 more common for multi-family branch circuits than 277/480 — verify the voltage system with your AHJ before applying it to a dwelling-unit calculation.

Why does the tool add 10A per spare space?

Reserving capacity for future circuits is standard sizing practice — since the load for an anticipated future circuit is undetermined, a common planning allowance is roughly 10A of headroom per reserved breaker space. This calculator lets you set the number of spare spaces to reserve (default 2) and adds that headroom before rounding to a standard load-center size.