Home Electrical Panel Load Capacity Calculator

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.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Home Electrical Panel Load Capacity Calculator

Calculate your home electrical panel's total load capacity, current connected load, and available headroom. Determine whether your panel can safely handle additional appliances or if an upgrade is needed.

Panel Main Breaker Rating (Amps)

60A (Older/Small Home) 100A (Standard) 150A (Medium Home) 200A (Modern Standard) 320A (Large Home / Dual Panel) 400A (Very Large Home)

Service Voltage

240V (Standard US Split-Phase) 120V (Single Phase)

### Connected Loads

Enter the wattage of your major appliances and systems. Leave blank or 0 if not applicable.

HVAC / Central Air Conditioner (Watts)

Typical: 2,000–5,000W for central AC

Electric Heating / Heat Pump (Watts)

Typical: 5,000–15,000W for electric furnace

Electric Water Heater (Watts)

Typical: 3,500–5,500W

Electric Dryer (Watts)

Typical: 4,000–6,000W

Electric Range / Oven (Watts)

Typical: 6,000–12,000W

EV Charger (Watts)

Level 2: 3,300–11,500W; Level 1: 1,440W

Dishwasher (Watts)

Typical: 1,200–2,400W

Refrigerator (Watts)

Typical: 100–400W running

Lighting (Watts)

Estimate total wattage of all lights

Other Loads (Watts)

Computers, TVs, small appliances, etc.

### Demand Factor Settings

NEC Demand Factor (%)

100% — No demand factor (worst case) 80% — Standard NEC residential demand 75% — Conservative estimate 65% — Aggressive demand reduction

NEC 220.83 allows demand factors for existing dwellings

Calculate Panel Load

function homCalc() { // --- Inputs --- var panelAmps = parseFloat(document.getElementById('hom-panel-amps').value); var voltage = parseFloat(document.getElementById('hom-voltage').value); var hvac = parseFloat(document.getElementById('hom-hvac').value) || 0; var heat = parseFloat(document.getElementById('hom-heat').value) || 0; var waterHeater = parseFloat(document.getElementById('hom-water-heater').value)|| 0; var dryer = parseFloat(document.getElementById('hom-dryer').value) || 0; var range = parseFloat(document.getElementById('hom-range').value) || 0; var ev = parseFloat(document.getElementById('hom-ev').value) || 0; var dishwasher = parseFloat(document.getElementById('hom-dishwasher').value) || 0; var refrigerator = parseFloat(document.getElementById('hom-refrigerator').value)|| 0; var lighting = parseFloat(document.getElementById('hom-lighting').value) || 0; var other = parseFloat(document.getElementById('hom-other').value) || 0; var demandPct = parseFloat(document.getElementById('hom-demand-factor').value);

// --- Validation --- var errors = []; if (isNaN(panelAmps) || panelAmps 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; return; }

// --------------------------------------------------------------- // CORE FORMULAS // --------------------------------------------------------------- // 1. Panel Total Capacity (VA / Watts at unity PF for resistive loads) // P_capacity = V × I_panel var panelCapacityW = voltage * panelAmps;

// 2. NEC 80% Continuous Load Rule // Panels must not be loaded beyond 80% of rated capacity for continuous loads // P_safe = P_capacity × 0.80 var safeCapacityW = panelCapacityW * 0.80;

// 3. Sum of all connected loads (raw, no demand factor) var totalConnectedW = hvac + heat + waterHeater + dryer + range + ev + dishwasher + refrigerator + lighting + other;

// 4. Apply NEC Demand Factor (NEC 220.83) // For existing dwellings: first 8,000W at 100%, remainder at 40% // We also apply the user-selected demand factor as a global multiplier // Demand Load = totalConnectedW × (demandPct / 100) var demandFactor = demandPct / 100; var demandLoadW = totalConnectedW * demandFactor;

// 5. NEC 220.83 Optional Calculation for existing dwellings // First 8,000W at 100%, balance at 40% var nec22083W; if (totalConnectedW 0; }) .sort(function(a,b){ return b.w - a.w; });

function fmt(n, dec) { dec = dec === undefined ? 0 : dec; return n.toLocaleString('en-US', { minimumFractionDigits: dec, maximumFractionDigits: dec }); }

function bar(pct) { var capped = Math.min(pct, 100); var color = pct ' + '' + '' + fmt(pct, 1) + '% of safe capacity'; }

var loadsTable = ''; if (loads.length > 0) { loadsTable = '' + '' + 'Appliance' + 'Watts' + 'Amps (' + voltage + 'V)' + '% of Panel' + ''; loads.forEach(function(l, i) { var bg = i % 2 === 0 ? '#fff' : '#f7fafc'; var amps = l.w / voltage; var pctPanel = (l.w / panelCapacityW) * 100; loadsTable += '' + '' + l.name + '' + '' + fmt(l.w) + 'W' + '' + fmt(amps, 1) + 'A' + '' + fmt(pctPanel, 1) + '%' + ''; }); loadsTable += ''; }

// --- Render --- resultDiv.style.display = 'block'; resultDiv.innerHTML = '## Panel Load Analysis '

' + 'Headroom: ' + fmt(headroomW_demand) + ' W / ' + fmt(headroomA_demand, 1) + ' A

' + bar(loadPctDemand) + '' + statusDemand.label + '

' + ''

' + 'Headroom: ' + fmt(headroomW_nec) + ' W / ' + fmt(headroomA_nec, 1) + ' A

' + bar(loadPctNec) + '' + statusNec.label + '

' + ''

' : '')

#### Formulas Used

1. Panel Total Capacity: Pcapacity = V × Ipanel e.g., 200A × 240V = 48,000W

2. NEC 80% Continuous Load Rule (NEC 210.20 / 230.42): Psafe = Pcapacity × 0.80 Panels must not be continuously loaded beyond 80% of rated capacity.

3. Demand Factor Method: Pdemand = Ptotal connected × Demand Factor Not all loads run simultaneously; demand factors account for diversity.

4. NEC 220.83 Optional Calculation (Existing Dwellings): PNEC = 8,000W + (Ptotal − 8,000W) × 0.40   (when Ptotal > 8,000W) First 8,000W at 100%, remainder at 40% demand factor.

5. Load Current: Iload = Pdemand / V

6. Available Headroom: Headroom (W) = Psafe − Pdemand Headroom (A) = (Ipanel × 0.80) − Iload

#### Assumptions & References

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