TryBuildCalcOffice Lighting Load Calculator (1.3 VA/ft² — No Demand Factor Reduction)
Calculate your office lighting load.
🕒 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: 3 × 20A @ 277V
For 10,000 ft² of Office / Bank — branch circuit design load 13,000 VA
General Lighting Load
Unit load: 1.30 VA/ft²
Connected load: 13,000 VA
Already includes the 125% continuous-load margin, per NEC Table 220.42(A)'s own note.
Branch Circuit Sizing
Circuit design load: 13,000 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: 13,000 VA
Total feeder/service demand: 13,000 VA (46.9 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 →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Lighting Load Calculator.
Office building lighting load sizing
Office and bank occupancies were combined into a single 1.3 VA/ft² unit lighting load under NEC Table 220.42(A), down substantially from older (pre-2020) editions' separate, higher office/bank figures — reflecting modern LED lighting efficiency. This figure already includes the 125% continuous-load margin.
Unlike dwellings, hospitals, hotels, and warehouses, office lighting load receives no Table 220.45 demand factor reduction at the feeder level — and since branch circuit count always uses the connected (not demand-reduced) load anyway, the full 13,000 VA sets the circuit count directly here.
- 10,000 ft² × 1.3 VA/ft² = 13,000 VA connected load, already 125%-inclusive.
- At 277V on 20A circuits (5,540 VA full capacity each), this needs 3 branch circuits.
- Edit the floor area above to match your actual office space for a precise circuit count.
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 | 10,000 ft² | Multiplied by the unit load for connected VA |
| Circuit | 20A @ 277V | Sets each circuit's usable capacity |
Step 1 — Connected Load
| Calculation | 10,000 × 1.30 |
| Connected load (125% already included) | 13,000 VA |
Step 2 — Feeder/Service Demand Load (Informational)
| Demand factor category | None — 100% of connected load |
| General lighting demand load | 13,000 VA |
| Total feeder/service demand (not used for circuit count) | 13,000 VA (46.9 A) |
Step 3 — Branch Circuit Design Load & Circuit Count
| Circuit design load (connected load, not demand-reduced) | 13,000 VA |
| Capacity per circuit | 20 × 277 = 5,540 VA |
| Circuits needed | ceil(13,000 ÷ 5,540) = 3 |
Therefore, for 10,000 ft² of Office / Bank, you need 3 circuits at 20A / 277V.
Related Calculators
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.