TryBuildCalc100 Amp Panel Calculator (Load Check for a 100A Dwelling Service)
Check your load against a 100A service.
🕒 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
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 14,020 VA total demand load at 240V (58.4A)
Load Breakdown (NEC 220.82 Optional Calculation)
| General lighting + receptacle load (1,200 sq ft × 3 VA) | 3,600 VA |
| Small-appliance circuits (2 × 1500 VA) | 3,000 VA |
| Laundry circuit(s) (1 × 1500 VA) | 1,500 VA |
| Water Heater | 4,500 VA |
| Dishwasher | 1,200 VA |
| Subtotal | 13,800 VA |
| After demand factor (100% of first 10,000 VA + 40% of remainder) | 11,520 VA |
| Heating/cooling load (Air Conditioning Only) | 2,500 VA |
| Total demand load | 14,020 VA |
Service Sizing
Total demand current: 58.4A
Recommended standard service: 100A
Headroom above calculated demand: 41.6A (41.6%)
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 →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Electrical Load / Panel Size Calculator.
100A panel load check
100A is NEC 220.82's minimum standard service size — this page is pre-set to a smaller home without electric space heating, a common scenario where 100A remains adequate.
Edit the inputs above to see how much headroom your actual smaller home has, or whether it pushes past 100A.
- 100A is the smallest service size NEC 220.82's Optional Calculation applies to.
- Homes without electric space heating (gas furnace, gas water heater) commonly stay comfortably within 100A.
- Adding electric space heat or a heat pump is the most common reason a 100A home needs to move up to 150A or 200A.
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 | 1,200 sq ft | Sets general lighting/receptacle load |
| Fixed Appliances | 2 appliances, 5,700 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 | 13,800 VA |
| After 10,000 VA / 40% demand factor | 11,520 VA |
| Heating/cooling load (Air Conditioning Only) | 2,500 VA |
| Total demand load | 14,020 VA |
Therefore, for 14,020 VA of total demand load at 240V (58.4A), you need a 100A service/panel.
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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.