Understanding Your Home's Electrical Load: Panel Sizing & NEC 220

Your breaker panel has a number stamped on the door, 100, 150, 200, and that number is the budget every circuit in the house draws against. A 2,000 square foot home starts at 10,500 VA of general lighting, small appliance, and laundry load before you plug in a single device, and the NEC demand factor drops it to 5,625 VA. Add an electric range, dryer, water heater, and central AC and the total lands near 14,000 VA, about 58 amps at 240 volts. That fits a 100 amp panel on paper and makes it a tight fit in practice, because the 80% margin eats the slack. Understand how the number is built and you can walk into a panel upgrade conversation knowing whether the electrician is selling you something you need or something they would rather sell. > **Find your load first:** Use our [free electrical load calculator](/electrical-load-calculator/), enter your square footage, appliance wattages, and HVAC loads, and it returns your total VA, amps, and a recommended panel size in seconds. --- ## What the Panel Number Actually Means The service size is the amount of current your home can draw from the utility through the main breaker. 100 amps at 240 volts is 24,000 watts of continuous capacity. 200 amps doubles that to 48,000 watts. The number is not a suggestion. Every breaker inside the panel is sized to it, and the main breaker protects the feed from the pole. Most homes built before 1980 have 100 amp service. New construction since the late 1990s has almost always been 200. The gap matters because the house of 1970 has a fraction of the electrical appetite of the same house today. A refrigerator, two TVs, and lights was the old baseline. Now add a microwave, dishwasher, garbage disposal, central AC, electric dryer, home office, and in a growing number of garages a Level 2 EV charger, and the panel that sailed through 1985 is running at the edge. ## Step 1: The General Load, Per NEC 220.41 The code builds the load calculation from the floor up. First is general lighting and receptacles, computed at **3 volt-amperes per square foot** of finished living space. A 2,000 square foot home is 6,000 VA. That single number covers every light fixture and every wall receptacle in the house, and it is a generous one. A fully loaded 15 amp circuit at 120 volts provides 1,800 VA, so the 6,000 VA figure is roughly three and a half busy circuits for the whole house. On top of that come the dedicated circuits the code requires: | Required Circuit | Count | VA Each | |------|:--:|:--:| | Kitchen / countertop small appliance (NEC 210.52) | 2 | 1,500 | | Laundry (NEC 210.52(F)) | 1 | 1,500 | The two kitchen circuits and the laundry circuit add 4,500 VA, taking the example home to 10,500 VA before demand factors. This is the starting number for every residential calculation, and most calculators, including [ours](/electrical-load-calculator/), pre-fill it for you. ## Step 2: The Demand Factor, Per NEC 220.42 The code then admits something you already know: nobody has every light on and every receptacle loaded at the same moment. The demand factor reduces the general load to a realistic number. | Portion of General Load | Demand Factor | |------|:--:| | First 3,000 VA | 100% | | 3,001 to 120,000 VA | 35% | | Above 120,000 VA | 25% | Run the 10,500 VA example through it: 3,000 VA at full, then 7,500 VA at 35% equals 2,625 VA, for a total of 5,625 VA. The general load is nearly cut in half, and that is by design. The panel is sized for what a house actually draws, not for the worst possible instant, because the wire and transformer feeding the neighborhood are sized the same way. ## Step 3: Fixed Appliances at Nameplate Ratings, Per NEC 220.53 Fixed appliances, range, oven, water heater, dryer, dishwasher, microwave, disposal, EV charger, are added at the **nameplate rating**, the wattage stamped on the label. Not the breaker size. A 50 amp range circuit is sized for the cable, and the range itself may draw 8,000 to 12,000 watts. The label, not the breaker, is the number that counts. If you have **four or more** fixed appliances, the code applies a 75% demand factor to their combined load. The reasoning is statistical: four appliances do not all draw their full rating at the same instant. The multiplier is small, but on a house with a range, dryer, water heater, and dishwasher it trims a meaningful chunk off the total. The wattage math is worth doing properly. If the label lists amps instead of watts, multiply amps by volts. A dryer pulling 20 amps at 240 volts is 4,800 watts. Guessing high adds dead load that pushes you toward a bigger panel. Guessing low undersizes the service, which is the more dangerous direction. ## Step 4: HVAC and the Largest Motor Rule, Per NEC 220.50 HVAC gets its own treatment because a compressor draws four to six times its running current for the first fraction of a second. The code handles it in two moves. First, include the **larger** of the heating or cooling load, never both, because they do not run at the same time. A heat pump in a mild climate may carry both labels, but only one runs. Second, add **25% of the largest motor** to cover the starting surge. For most homes the AC compressor is that largest motor, typically 3,000 to 6,000 watts for a 3 to 5 ton unit. A pool pump, hot tub, or a large exhaust fan takes over the role in a house without central AC. The 25% adder is small, but the rule is mandatory, and skipping it is one of the most common mistakes on submitted load worksheets. ## Amps, the 80% Rule, and Choosing a Panel Once the total VA is assembled, divide by your service voltage to get amps. **Amps = Total VA ÷ Volts.** A 13,350 VA home at 240 volts is about 56 amps. The 80% rule is the safety margin the code builds in for continuous loads, loads that run for three hours or more, like baseboard heat, water heaters, and EV chargers. A panel is not meant to run at its full rating continuously, so the calculated load must not exceed **80% of the panel's rated capacity**. A 100 amp panel safely serves 80 amps of continuous load. A 200 amp panel serves 160. The rule is why the recommendation matters more than the raw math. A home that calculates to 95 amps fits a 100 amp panel per the letter of the code, but it runs the panel at the edge of its margin and leaves no room for a future dryer, a second fridge, or anything the family buys next year. Most electricians size that home at 150 or 200 amps, not because the math demands it, but because the budget for headroom is cheap compared to a second upgrade. | Panel Size | What It Comfortably Serves | |------|------| | **100A** | Homes under 1,500 sq ft with gas heat, gas water heater, gas range, no EV charger | | **150A** | Medium homes, 1,500 to 2,500 sq ft, some electric appliances, central AC | | **200A** | The modern standard: up to 3,500 sq ft, full electric appliances, AC, pool, one EV charger | | **400A** | Large custom homes, two EV chargers, workshops, all-electric over 4,000 sq ft | ## When You Actually Need to Run the Numbers Most homeowners meet a load calculation for the first time when something trips: the AC and dryer on the same leg, or lights dimming when the microwave kicks on. Those are symptoms, not the diagnosis. Run the calculation before four situations in particular. **Adding an EV charger.** A Level 2 charger draws 32 to 48 amps continuously, which is 40 to 60% of a 100 amp panel's capacity all by itself. This is the single most common reason a modern home needs a service upgrade. **Finishing a basement.** The new receptacles, lighting, and a second fridge or microwave all come out of the same panel. A basement finish that adds a bathroom even brings a new circuit count. **Installing a hot tub.** Many hot tubs require a dedicated 50 or 60 amp circuit. The spa plus everything already running can push a 100 amp panel over its number. **Switching from gas to electric.** An electric range alone adds 40 to 50 amps of demand. Electric water heaters, dryers, and heat pumps each add their own share, and the switch usually comes with a panel recommendation in the same sentence. In all four cases the load calculation tells you whether you need the upgrade before the electrician starts. The alternative is a mid-project phone call: work stops because the panel cannot take the load, and the $3,000 to $5,000 upgrade becomes an emergency line item instead of a planned one. ## 5 Load Calculation Mistakes That Fail Inspection ### 1. Using Breaker Size Instead of Nameplate Rating A 50 amp range circuit is not a 50 amp load. The range's nameplate says 8,000 to 12,000 watts, and that is the number the worksheet wants. Sizing the load off the breaker inflates the total and can push a 200 amp service onto paper when the house barely needs 150. ### 2. Adding the Largest Motor Twice The 25% motor adder applies to the largest motor only. Some worksheets add it to the AC and then again to the pool pump or the sump pump. Pick the single largest motor, apply the 25%, and stop. ### 3. Counting Heat and Cool Both A home with a furnace and central AC has two HVAC loads on paper, but only one runs at a time. Including both can add 5,000 to 15,000 VA of phantom load. The code takes the larger of the two, never the sum. ### 4. Forgetting the 80% Rule on the Panel Calculating 95 amps and concluding a 100 amp panel works is correct math and wrong engineering. Continuous loads push the panel past its margin, and inspectors and insurance companies both care. Sizing to 80% of capacity, not 100%, is the rule. ### 5. Ignoring the Future A load calculation is a snapshot of today, and the panel you install is for ten years from now. An EV charger, a heat pump, a second refrigerator, or a home office can each add thousands of VA. Building headroom into the panel size on day one costs a few hundred dollars. Doing a second upgrade costs a few thousand and a weekend without power. --- Ready to size your panel? Use our [free electrical load calculator](/electrical-load-calculator/) to run the NEC 220 method on your home in one pass: general load, demand factors, appliances, HVAC, total VA, amps, and a recommended panel size. Pairing the result with HVAC loads? The [HVAC BTU calculator](/hvac-btu-calculator/) sizes the heating and cooling equipment first, which sets the number you enter for the AC. Finishing the basement that just changed your load? The [drywall installation guide](/blog/2026-07-24-drywall-installation-guide/) covers the sheets and mud behind those new receptacles, and if the new load lands in the garage, the [concrete slab pouring guide](/blog/2026-08-04-concrete-slab-pouring-guide/) has the slab your EV charger will sit on.