TryBuildCalcLighting Load Calculator (NEC 220.12/220.42 — General Lighting Load)
Calculate your lighting load instantly.
🕒 Last updated: August 29, 2026
Inputs
ℹ️Sets the NEC Table 220.42 unit lighting load (VA/ft²) and whether a demand factor reduction applies.
ℹ️Measured from outside building dimensions per NEC 220.12/220.42, not usable/carpet area.
Show Window Lighting
Track Lighting
Circuit Sizing
Cost
Branch Circuits Needed: 2 × 20A @ 277V
For 5,000 ft² of Office / Bank — branch circuit design load 6,500 VA
General Lighting Load
Unit load: 1.30 VA/ft²
Connected load: 6,500 VA
Already includes the 125% continuous-load margin, per NEC Table 220.42(A)'s own note.
Branch Circuit Sizing
Circuit design load: 6,500 VA
Capacity per circuit: 5,540 VA (20A × 277V, full rating)
Uses the connected load, not the demand-reduced feeder load below — branch circuits don't get diversity with each other.
Feeder / Service Demand Load (Informational)
After Table 220.45 demand factor: 6,500 VA
Total feeder/service demand: 6,500 VA (23.5 A)
This is the load a feeder/service supplying this space would need to carry — not the same figure as the branch circuit design load above, and not used for the circuit count.
Assumptions Used
NEC 2023 220.12/Table 220.42(A) (general lighting unit loads — default method, not the optional 220.42(B) energy-code alternate), Table 220.45 (feeder/service demand factors), 220.46(A)/(B) (show window/track lighting). Branch circuit count uses the connected (non-demand-factor-reduced) load, since demand factors apply to feeder/service sizing only. Single-phase VA/voltage estimate — a genuine 3-phase panel schedule needs per-phase balancing beyond this calculator's scope. This is a reference estimate — confirm with a licensed electrician before installation.
Checking your panel has enough total capacity for this plus everything else? Panel Size Calculator →
Need to size the wire and breaker for one of these circuits? Wire Size Calculator →
What Is a Lighting Load Calculator?
A lighting load calculator finds the general lighting demand load for a building and the number of branch circuits needed to carry it, using the NEC's occupancy-specific unit lighting loads (Table 220.42) and demand factors (Table 220.45) — the code method used to size lighting feeders and services.
Unlike a dwelling-only whole-service calculator, this tool supports several occupancy types — offices, retail stores, restaurants, schools, gymnasiums, hospitals, hotels/motels, and storage warehouses — each with its own NEC-specified unit load and, where the code allows it, its own demand factor reduction. It also handles show window and track lighting (NEC 220.46) as separate, non-reduced add-on loads.
Why getting this right matters:
- Using the wrong occupancy's unit load can significantly over- or under-size the lighting circuits
- Demand factors reduce feeder/service sizing only — using them to size branch circuit count under-sizes the actual number of circuits needed
- Show window and track lighting are easy to forget, and both add real load beyond general lighting
- Circuit voltage (120V vs. 277V) meaningfully changes how many circuits a given load actually needs
Lighting Load Formula: How Is It Calculated?
This calculator computes two different totals: a feeder/service demand load (informational) and a branch circuit design load (what actually sets the circuit count) — they are not the same figure, and using the wrong one under- or over-sizes the result.
Step 1 — Connected Lighting Load
Connected Load (VA) = Floor Area (ft²) × Unit Load (VA/ft²)
The unit load comes from NEC Table 220.42(A) (or 220.12 for dwelling units) based on your occupancy type. Per Table 220.42(A)'s own note, this figure already includes the NEC 210.20(A) 125% continuous-load multiplier — no additional factor is applied to it anywhere below.
Step 2 — Feeder/Service Demand Load (Informational Only)
Feeder Demand = (Connected Load × Table 220.45 demand factor) + Show Window Design VA + Track Lighting Design VA
(demand factor applies to dwelling, hospital, hotel/motel, and warehouse only — all others: 100%)
Only certain occupancies receive a demand factor reduction, applied in tiers to different VA brackets — this reduction reflects that not every circuit in a large building draws its full load at once, from the perspective of the feeder/service supplying all of them together.
Step 3 — Branch Circuit Design Load & Circuit Count
Circuit Design Load = Connected Load + Show Window Design VA + Track Lighting Design VA
Circuits Needed = ceil(Circuit Design Load ÷ (Breaker A × Voltage))
Circuit count uses the CONNECTED load, not the demand-reduced feeder figure — demand factors are a feeder/service tool only; individual branch circuits don't get diversity with each other and must each be sized for their own actual assigned load (NEC 210.19). Show window (200 VA/ft) and track lighting (150 VA per 2 ft) come from NEC 220.46, are never demand-factor-reduced, and — since no note exempts them the way Table 220.42(A) is exempted — get their own explicit ×1.25 continuous-load factor (their "Design VA") before being added in. Because both totals are already fully design-value-inclusive, circuit capacity uses the breaker's full rating with no further 80%/125% adjustment.
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 |
|---|---|---|
| Occupancy | Office / Bank (1.30 VA/ft²) | Sets the unit lighting load and demand factor category |
| Floor Area | 5,000 ft² | Multiplied by the unit load for connected VA |
| Circuit | 20A @ 277V | Sets each circuit's usable capacity |
Step 1 — Connected Load
| Calculation | 5,000 × 1.30 |
| Connected load (125% already included) | 6,500 VA |
Step 2 — Feeder/Service Demand Load (Informational)
| Demand factor category | None — 100% of connected load |
| General lighting demand load | 6,500 VA |
| Total feeder/service demand (not used for circuit count) | 6,500 VA (23.5 A) |
Step 3 — Branch Circuit Design Load & Circuit Count
| Circuit design load (connected load, not demand-reduced) | 6,500 VA |
| Capacity per circuit | 20 × 277 = 5,540 VA |
| Circuits needed | ceil(6,500 ÷ 5,540) = 2 |
Therefore, for 5,000 ft² of Office / Bank, you need 2 circuits at 20A / 277V.
Essential Checklist+−
Complete these critical checks before approving the work or proceeding to the next construction stage.
✓Occupancy & Floor Area Input Accuracy+-
- Correct occupancy classification selected, matching the building's actual use
- Floor area measured per NEC's outside-dimensions rule, not usable/carpet area
✓NEC Demand Factor & Load Calculation+-
- Demand factor category confirmed correct for the occupancy — not every occupancy gets a reduction
- Tiered demand factor brackets applied to the correct VA ranges, not a flat percentage of the whole load
- Connected load (before demand factor) used for branch circuit count; demand load (after) used for feeder/service sizing only — not swapped
- Hospital/hotel areas with lighting on continuously (operating rooms, ballrooms, dining rooms) excluded from the demand factor reduction
✓Show Window & Track Lighting+-
- Show window and track lighting loads confirmed never reduced by the Table 220.45 demand factor
✓Branch Circuit Sizing & Code Compliance+-
- Circuit voltage selection matches the actual electrical system serving the space
- 80% continuous-load branch circuit rule confirmed applied, not skipped
- AFCI/GFCI protection requirements checked separately for the specific circuits and locations involved
- Licensed electrician review required before installation, not a substitute for professional design
Full QC Checklist+−
Verification checklist for general lighting load sizing — covering occupancy/floor area input accuracy, NEC demand factor and load calculation, show window/track lighting, and branch circuit sizing/code compliance. Use the Essential Checklist for critical checks before installation; expand to Full QC Checklist for complete verification.
✓Occupancy & Floor Area Input Accuracy+-
- Correct occupancy classification selected, matching the building's actual use
- Floor area measured per NEC's outside-dimensions rule, not usable/carpet area
- Mixed-occupancy building split into separate calculations per occupancy area, not averaged
- Custom VA/ft² value (if used) sourced from the actual NEC table for an occupancy not listed here
- Future use, tenant changes, or expansion considered before finalizing circuit count
✓NEC Demand Factor & Load Calculation+-
- Demand factor category confirmed correct for the occupancy — not every occupancy gets a reduction
- Tiered demand factor brackets applied to the correct VA ranges, not a flat percentage of the whole load
- Connected load (before demand factor) used for branch circuit count; demand load (after) used for feeder/service sizing only — not swapped
- Hospital/hotel areas with lighting on continuously (operating rooms, ballrooms, dining rooms) excluded from the demand factor reduction
- Single-phase VA/voltage estimate recognized as a planning figure, not a substitute for a real 3-phase panel schedule
✓Show Window & Track Lighting+-
- Show window length measured horizontally along its base, not window height or perimeter
- Show window and track lighting loads confirmed never reduced by the Table 220.45 demand factor
- Track lighting length includes the full total of all track runs in the space, not just one section
- Track lighting exemption checked for dwelling units and hotel/motel guest rooms
- Multicircuit track lighting load distributed evenly across its supply circuits, not loaded onto one
✓Branch Circuit Sizing & Code Compliance+-
- Circuit voltage selection matches the actual electrical system serving the space
- 80% continuous-load branch circuit rule confirmed applied, not skipped
- Breaker size selection matches what's actually available/planned in the panel
- Circuits evenly distributed and balanced across the panel/phases, not concentrated in one area
- AFCI/GFCI protection requirements checked separately for the specific circuits and locations involved
- Licensed electrician review required before installation, not a substitute for professional design
NEC Unit Lighting Loads by Occupancy
NEC Table 220.42(A) (non-dwelling, default method) and 220.12 (dwelling) unit loads and Table 220.45 demand factor category, for the occupancy types supported by this calculator. These reflect the ASHRAE/IECC-aligned reconstruction of this table starting with the 2020 NEC cycle — most occupancies dropped substantially from older editions; a few (marked below) reportedly increased and could not be independently re-confirmed with full confidence.
| Occupancy | Unit Load (VA/ft²) | Demand Factor Applies? |
|---|---|---|
| Dwelling Unit | 3.0 | Yes — tiered (100% / 35% / 25%) |
| Office / Bank | 1.3 | No — 100% |
| Retail Store | 1.9 | No — 100% |
| Restaurant | 1.5 | No — 100% |
| School | 1.5 | No — 100% |
| Gymnasium | 1.7 (unverified — reportedly increased) | No — 100% |
| Hospital | 1.6 | Yes — tiered (40% / 20%) |
| Hotel / Motel (Guest Rooms) | 1.7 | Yes — tiered (50% / 40% / 30%) |
| Warehouse (Storage) | 0.25 (unverified — reportedly increased) | Yes — tiered (100% / 50%) |
When should you use this lighting load calculator?
- Sizing general lighting branch circuits for a new commercial or residential building.
- Checking whether an existing lighting circuit plan meets NEC demand load requirements.
- Comparing circuit counts across different occupancy types or floor areas.
- Including show window or track lighting load in a retail lighting design.
- Comparing 120V vs. 277V circuit counts for a commercial lighting plan.
Quick Lighting Load Sizing Tips
- Use outside building dimensions for floor area, not usable/carpet area.
- Split a mixed-occupancy building into separate calculations per area rather than averaging.
- Remember show window and track lighting are calculated separately and always added at full value.
- Match circuit voltage to your actual electrical system — 277V is standard for larger commercial buildings.
- Leave spare circuit capacity if future tenant changes or expansion are likely.
Common Mistakes
- Applying a demand factor reduction to an occupancy that doesn't get one (offices, retail, restaurants, schools, gymnasiums).
- Using the demand-reduced feeder/service figure to determine branch circuit count — branch circuits don't get diversity with each other and must use the connected load.
- Applying an additional continuous-load factor to the general lighting VA — Table 220.42(A)'s unit loads already include it, per the table's own note.
- Using usable/carpet area instead of outside building dimensions for floor area.
- Skipping a separate AFCI/GFCI protection check, assuming circuit sizing alone covers code compliance.
Limitations
- Covers common occupancy classifications only, not the NEC's full occupancy list — use Custom for others.
- The Gymnasium and Warehouse (Storage) unit loads could not be independently re-confirmed with full confidence against the post-2020 NEC table reconstruction (multiple sources report these two occupancies increased rather than decreased, but a precise current figure wasn't verifiable from available sources) — verify these two specifically against your current code text, or use Custom.
- Always uses the default NEC 220.42(A) unit-load table — does not model the separate, optional 220.42(B) energy-code alternate method, which allows lower (energy-code-referenced) unit loads but only if the building complies with an adopted energy code and has a power-monitoring system with load alarms installed.
- Does not exclude hospital/hotel areas where lighting is used continuously (operating rooms, ballrooms) — calculate those separately at 100%.
- Single-phase VA/voltage estimate only — a genuine 3-phase panel schedule needs per-phase load balancing beyond this calculator's scope.
- Does not determine AFCI/GFCI protection requirements, which depend on circuit type and location.
- This is a planning reference estimate, not a substitute for a licensed electrician's review.
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.