TryBuildCalcElectrical Load / Panel Size Calculator (NEC 220.82 Optional Calculation)
Calculate service/panel size instantly.
🕒 Last updated: August 27, 2026
Inputs
ℹ️Outside-dimension floor area per NEC 220.82 — excludes open porches, garages, and unfinished/unused spaces not adaptable for future use.
ℹ️NEC 220.52(A) requires a minimum of 2 (1,500 VA each) — this calculator enforces that floor automatically.
ℹ️NEC 220.52(B) requires a minimum of 1 (1,500 VA) — this calculator enforces that floor automatically.
Fixed-in-Place Appliances
Include every permanently connected appliance — range, dryer, water heater, dishwasher, disposal, and similar — at full nameplate VA/watts. Don't include portable, cord-and-plug appliances.
Appliance 1
Appliance 2
Appliance 3
Heating / Cooling
ℹ️NEC 220.82(C) uses only the larger of heating or cooling load, never both added together.
Cost
Recommended Service/Panel Size: 100A
From 20,900 VA total demand load at 240V (87.1A)
Load Breakdown (NEC 220.82 Optional Calculation)
| General lighting + receptacle load (2,000 sq ft × 3 VA) | 6,000 VA |
| Small-appliance circuits (2 × 1500 VA) | 3,000 VA |
| Laundry circuit(s) (1 × 1500 VA) | 1,500 VA |
| Range | 8,000 VA |
| Dryer | 5,500 VA |
| Water Heater | 4,500 VA |
| Subtotal | 28,500 VA |
| After demand factor (100% of first 10,000 VA + 40% of remainder) | 17,400 VA |
| Heating/cooling load (Air Conditioning Only) | 3,500 VA |
| Total demand load | 20,900 VA |
Service Sizing
Total demand current: 87.1A
Recommended standard service: 100A
Headroom above calculated demand: 12.9A (12.9%)
Assumptions Used
NEC 220.82 Optional Calculation for dwelling units — a single 120/240V or 208Y/120V service ≥100A. Heating and cooling loads are never added together, only the larger is used. This is a reference estimate — confirm with a licensed electrician before final installation.
Sizing an individual circuit's breaker next? Circuit Breaker Size Calculator →
Need the feeder or service wire size for this load? Wire Size Calculator →
What Is an Electrical Load / Panel Size Calculator?
An electrical load / panel size calculator estimates the correct service or panel amperage for an entire dwelling unit, using the NEC 220.82 Optional Calculation — the standard, widely-used simplified method for sizing a single dwelling's service (100A or larger) from its floor area, fixed appliances, and heating/cooling load.
This is a whole-house, service-level calculation — different in scope from the Circuit Breaker Size Calculator (one circuit at a time) and the Wire Size Calculator (one wire run at a time). Use this tool first to find the right service size, then size individual circuits and wires within it with those calculators.
Why getting service size right matters:
- An undersized service can't safely support the dwelling's actual connected load, and won't leave room for future additions like an EV charger
- An oversized service costs more upfront than necessary — utility, panel, and conductor costs all scale with amperage
- Heating/cooling loads are commonly the single biggest swing factor, and are easy to get wrong by adding both instead of taking only the larger
- This is genuinely different math from circuit-level breaker sizing — a whole-panel calculation uses demand factors across many circuits and appliances at once
Panel Size Formula: How Is Service Size Calculated?
NEC 220.82 combines a general load subtotal (subject to one demand factor) with a separate heating/cooling load, then rounds the total current up to a standard service size.
Step 1 — General Load Subtotal
General Load = (Floor Area × 3 VA) + (Small-Appliance Circuits × 1,500 VA)
+ (Laundry Circuits × 1,500 VA) + Sum of Fixed Appliance Nameplate VA
Per NEC 220.82(B), general lighting/receptacle load, small-appliance and laundry circuits, and every fixed-in-place appliance (including range and dryer, at full nameplate VA) are all summed into one subtotal.
Step 2 — Apply the Demand Factor
General Demand = 100% of first 10,000 VA + 40% of the remainder above 10,000 VA
This single demand factor reflects that not every load in the general subtotal runs at full power simultaneously — it's applied to the general subtotal only, before the heating/cooling load is added.
Step 3 — Add the Larger of Heating or Cooling
Total Demand = General Demand + MAX(Heating Load, Cooling Load)
Per NEC 220.82(C), heating and cooling are never added together — only the larger of the two is included, since a dwelling's heating and cooling equipment isn't assumed to run simultaneously.
Step 4 — Convert to Current and Round to a Standard Size
Total Demand Current = Total Demand (VA) ÷ Voltage
Recommended Service = smallest standard size ≥ Total Demand Current
Standard dwelling service sizes (100, 125, 150, 200, 225, 300, 400A) come from what's actually manufactured and installed — the calculated current is always rounded up, never down.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Floor Area | 2,000 sq ft | Sets general lighting/receptacle load |
| Fixed Appliances | 3 appliances, 18,000 VA | Added to general subtotal before demand factor |
| HVAC | Air Conditioning Only | Sets the heating/cooling load added after demand factor |
Steps 1-2 — General Load and Demand Factor
| Calculation | Result |
|---|---|
| General load subtotal | 28,500 VA |
| After 10,000 VA / 40% demand factor | 17,400 VA |
| Heating/cooling load (Air Conditioning Only) | 3,500 VA |
| Total demand load | 20,900 VA |
Therefore, for 20,900 VA of total demand load at 240V (87.1A), you need a 100A service/panel.
Essential Checklist+−
Complete these critical checks before approving the work or proceeding to the next construction stage.
✓Load Input Accuracy+-
- Floor area measured per NEC 220.82's definition, not total lot or footprint area
- Every fixed-in-place appliance entered at its actual nameplate VA/watt rating, not an estimate
- HVAC nameplate VA/amps used directly, not converted from a BTU rating with an assumed efficiency
✓Demand Factor Application+-
- 10,000 VA / 40% demand factor confirmed applied to the general load subtotal, not the final total
- Only the larger of heating or cooling load included, never both added together
- Fixed appliances (including range/dryer) entered once at full nameplate VA, not also run through separate demand tables
✓HVAC & Load Selection+-
- HVAC configuration selected matches the actual equipment installed, not a default guess
✓Service Sizing & Code Compliance+-
- Final service size confirmed as a genuine standard size, rounded up from the calculated demand current
- Confirmed the dwelling qualifies for a 100A-or-larger single service — not a smaller sub-100A legacy service
- Confirmed this is a single dwelling unit on one service — not a duplex, multi-family, or commercial building
- Confirmed this is a new/full-recalculation scenario, not an existing-service load-addition check (NEC 220.83)
- Service sizing reviewed by a licensed electrician, and permit/utility coordination requirements confirmed
Full QC Checklist+−
Verification checklist for dwelling-unit service/panel sizing under the NEC 220.82 Optional Calculation — covering load input accuracy, demand factor application, HVAC load selection, and service sizing/code compliance. Use the Essential Checklist for critical checks before finalizing a service size; expand to Full QC Checklist for complete verification.
✓Load Input Accuracy+-
- Floor area measured per NEC 220.82's definition, not total lot or footprint area
- Every fixed-in-place appliance entered at its actual nameplate VA/watt rating, not an estimate
- Small-appliance and laundry circuit counts match the actual planned circuits, not just the code minimum
- HVAC nameplate VA/amps used directly, not converted from a BTU rating with an assumed efficiency
- All fixed-in-place appliances included, not just the range and dryer
✓Demand Factor Application+-
- 10,000 VA / 40% demand factor confirmed applied to the general load subtotal, not the final total
- Only the larger of heating or cooling load included, never both added together
- Heat pump with supplemental electric heat uses 100% compressor + 65% supplemental, confirmed against equipment specs
- Electric space heating demand factor (65% vs. 40%) matches the actual count of separately controlled heating units
- Fixed appliances (including range/dryer) entered once at full nameplate VA, not also run through separate demand tables
✓HVAC & Load Selection+-
- HVAC configuration selected matches the actual equipment installed, not a default guess
- "Both A/C and Separate Electric Heat" selected whenever both systems genuinely coexist
- Only the single largest heating/cooling system's nameplate used, not summed across multiple independent units
- Reasonably foreseeable future loads (EV charger, hot tub, workshop) considered against the headroom shown
✓Service Sizing & Code Compliance+-
- Final service size confirmed as a genuine standard size, rounded up from the calculated demand current
- Confirmed the dwelling qualifies for a 100A-or-larger single service — not a smaller sub-100A legacy service
- Confirmed this is a single dwelling unit on one service — not a duplex, multi-family, or commercial building
- Confirmed this is a new/full-recalculation scenario, not an existing-service load-addition check (NEC 220.83)
- Calculated headroom above demand load reviewed and considered adequate for the project's needs
- Service sizing reviewed by a licensed electrician, and permit/utility coordination requirements confirmed
Standard Dwelling Service Sizes
Standard residential service/panel amperage ratings actually sold and installed — a service size always rounds up to one of these, never to a custom in-between value.
| Standard Sizes (A) | Typical Use |
|---|---|
| 100 | Minimum size under NEC 220.82; smaller homes without electric heat |
| 125, 150 | Mid-size homes, some electric appliances |
| 200 | Most common size for a modern single-family home |
| 225, 300 | Larger homes or homes with substantial electric heat/HVAC load |
| 400 | Large or all-electric homes with heavy appliance/HVAC load (this calculator's upper limit) |
When should you use this panel size calculator?
- Sizing a new dwelling's electrical service during design or permitting.
- Fully re-evaluating an existing home's service as part of a complete rewire or major renovation.
- Checking whether a planned major addition (electric heat, a heat pump, a larger kitchen) needs a bigger service.
- Comparing service size needs across different HVAC configurations (gas vs. electric heat vs. heat pump).
- Getting a planning-stage estimate before a licensed electrician performs the official load calculation.
Quick Panel Sizing Tips
- Use actual nameplate ratings for every fixed appliance — don't estimate from memory.
- Never add heating and cooling load together — only the larger of the two counts.
- Consider near-term future loads (EV charger, hot tub, workshop) against the calculated headroom before finalizing.
- Electric space heating and heat pumps are usually the single biggest driver toward a larger service — get their nameplate ratings right.
- This is a planning estimate — get the official load calculation and service design from a licensed electrician before finalizing.
Common Mistakes
- Adding heating and cooling loads together instead of taking only the larger, per NEC 220.82(C).
- Applying a separate range/dryer demand table on top of this calculator's result — the Optional Method already bundles them into the general appliance bucket at full nameplate VA.
- Using an existing-service load-addition shortcut (NEC 220.83) for what's actually a from-scratch new-service calculation, or vice versa.
- Forgetting smaller fixed appliances (disposal, dishwasher, built-in microwave) and only counting the range, dryer, and water heater.
- Rounding the service size down to save cost instead of up to the next standard size.
Limitations
- Implements NEC 220.82 (Optional Calculation) only — sizing a service from scratch for a single dwelling unit. It does not implement NEC 220.83 (checking whether an existing, already-loaded service has room for one added load).
- Scoped to one dwelling unit on a single 120/240V or 208Y/120V service — not multi-family, mixed-use, or commercial buildings, which use different Article 220 methods.
- Minimum recommended service is 100A, matching NEC 220.82's defined scope — not intended for evaluating smaller legacy services.
- NEC-based only (US) — other regions use different service-sizing standards and conventions and this calculator does not model them.
- This is a planning reference estimate, not a substitute for a licensed electrician's official load calculation and service design.
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.