Home Electrical Load Calculator
Sum the kW of your major appliances to estimate peak and average household load. The result feeds directly into panel, solar, and generator sizing.
Common conversions
| Input | Result |
|---|---|
| 2-bedroom home, 30 A / 240 V service | 7.2 kW |
| 3-bedroom home, 45 A / 240 V service | 10.8 kW |
| 100 A panel, max continuous capacity | 24 kW |
| 150 A panel, max continuous capacity | 36 kW |
| 200 A panel, max continuous capacity | 48 kW |
| Central AC compressor, 15-45 A @ 240 V | 3.6-10.8 kW |
| Electric range, nameplate | 8-12 kW |
| Electric dryer | 5 kW |
| Electric water heater (tank) | 4.5 kW |
| Level 2 EV charger | 7.7-11.5 kW |
The math behind it
- Nameplate sum = 12 + 5 + 4.5 + 6 + 7.7 + 3 = 38.2 kW
- Apply a simplified diversity rule: first 10 kW at 100%, remainder at 40%
- 10 + (28.2 × 0.4) = 10 + 11.28 = 21.28 kW
Everything you need to know
Adding up the nameplate rating of every appliance in a house always overstates what the panel actually has to deliver. The National Electrical Code solves this with demand factors, and understanding them is the difference between a load calculation that gets a permit approved and one that gets kicked back.
NEC demand factors: why appliances do not add up directly
NEC Article 220 does not ask you to sum every circuit at full nameplate rating. Instead it applies diversity: general lighting and receptacle load is calculated at 3 volt-amps per square foot, small-appliance and laundry circuits add fixed amounts, and then a sliding demand factor is applied to the total. For a dwelling unit, the first 10 kVA of general load is counted at 100%, and everything above that is counted at just 40%. Four or more fixed appliances (dishwasher, disposal, water heater, dryer) get their own 75% demand factor. This is why a home with 38 kW of nameplate appliances might have a code-calculated demand of only 21 kW. The logic holds up in practice: an oven, a dryer, and central air rarely hit full draw at the exact same minute.
Panel sizing: 100 A, 150 A, and 200 A service
Service size is just amperage at your utility voltage, so at 240 V a 100 A panel caps out at 24 kW, a 150 A panel at 36 kW, and a 200 A panel at 48 kW. Older homes with gas heat and a gas range often get by fine on 100 A. Modern all-electric homes with a heat pump, electric range, and an EV charger frequently push diversified demand past 20 kW, which leaves little headroom on a 100 A service once safety margin is factored in. That is why most new construction and major electrification projects now spec 150 A or 200 A panels. If you are close to your service limit and want to add a heat pump or EV charger, an electrician can run a proper NEC 220 load calculation to confirm whether you need a full service upgrade or whether a load-management device (which shares capacity between circuits) will do the job for less money.
Adding up circuits vs. realistic peak demand
There is a real difference between the nameplate sum (every device at maximum draw simultaneously, which almost never happens) and the diversified peak (what the house actually pulls at its worst realistic moment). For permit work, use the NEC demand-factor method or have a licensed electrician run it. For sizing a generator or a solar-plus-battery system, a simpler rule of thumb works well: take the nameplate sum and divide by 2 to 3, since HVAC cycles on and off, the oven runs a fraction of the day, and laundry and cooking rarely overlap with a full HVAC run. Both numbers matter for different jobs, so keep them separate rather than picking whichever one is more convenient.
Common applications
Compare your diversified peak demand against your existing panel's kW ceiling to see whether a 100 A to 200 A upgrade is actually necessary before paying an electrician for one.
Whole-house generators are sized to the realistic peak, not the nameplate sum. Divide your nameplate total by 2-3 to get a starting point, then confirm with a licensed installer.
Annual usage in kWh drives solar array size, but your diversified peak kW tells a battery installer how much power the battery bank needs to deliver during an outage.
Before committing to a new 240 V circuit, check whether your current diversified demand plus the new load fits under your panel's rated capacity with 20% headroom to spare.
Common mistakes
Summing every appliance at full nameplate rating overstates real demand by 40-60% and can lead to an unnecessary and expensive service upgrade.
EV chargers and other loads that run 3+ hours continuously need to be sized at 125% of their rated draw for breaker and conductor selection, not the raw nameplate figure.
A 200 A main breaker does not guarantee a 200 A busbar if the panel was built for a smaller main. Check the panel's label, not just the breaker, before assuming available capacity.
Adding a heat pump or EV charger without a proper NEC 220 load calculation risks an overloaded panel that trips breakers under real-world peak conditions, or a failed inspection.
Frequently asked questions
How many kW does a typical house use at peak?+
Most all-electric 3-bedroom homes peak around 15-20 kW after demand factors are applied, even though the nameplate ratings of every appliance combined might add up to 35-40 kW.
Is a 100 A panel enough for an all-electric home?+
No. A 100 A panel tops out at 24 kW at 240 V, which is tight once you add an electric range, water heater, dryer, and heat pump. Most new all-electric builds spec 150 A or 200 A service instead.
Do I need a permit to add a major electrical load?+
Yes. Adding a subpanel, an EV charger circuit, or a heat pump typically requires a permit and, in most jurisdictions, an NEC Article 220 load calculation showing the panel can handle the addition safely.
What is a demand factor?+
A demand factor is a percentage the NEC applies to a load category to reflect that not everything runs at once. The first 10 kVA of general dwelling load counts at 100%, and the remainder counts at 40%, which is why code-calculated demand is always lower than a raw nameplate sum.
How much spare capacity should I leave on a panel?+
Leave at least 20% headroom above your calculated diversified peak. On a 200 A (48 kW) panel, that means keeping calculated demand under roughly 38 kW so you have room for a future EV charger or heat pump without a service upgrade.
Can I add an EV charger without upgrading my panel?+
Often yes. A load-management device can share capacity with your dryer or range circuit and cap the charger's draw when other big loads are running, avoiding a full service upgrade in many homes with 100-150 A panels.
Why is my nameplate total so much higher than my utility bill implies?+
Nameplate ratings assume every device runs at full output continuously. In reality your oven heats in cycles, your AC compressor cycles on and off, and most circuits sit idle most of the day, so actual usage is a fraction of the nameplate sum.
How does home electrical load feed into solar or generator sizing?+
Solar and generator sizing both start from your diversified peak, not the nameplate sum. A home with a 20 kW diversified peak might need only an 8-10 kW solar array sized against annual kWh, but a generator meant to run the whole house during an outage should cover close to that 20 kW peak.
What is the difference between a 150 A and 200 A service?+
At 240 V, a 150 A service delivers 36 kW and a 200 A service delivers 48 kW. The extra 12 kW of headroom on a 200 A panel is usually the deciding factor for homes planning to add a heat pump, EV charger, or both.