Overall demand factor
72%
Load & Demand Calculation Calculator
Build a load schedule from connected loads and demand factors, then derive the calculated demand (kW/kVA), demand current and a recommended transformer rating.
Result
Enter your load → get a full design & BOM in seconds
Sample outputCalculated demand load
83.2 kW
97.9 kVA at PF 0.85 · connected 145.0 kW · Ks 0.8
Demand current
141 A
Transformer
160 kVA
Load factor
61%
Load schedule
| Load group | Connected kW | Demand factor | Demand kW |
|---|---|---|---|
| Lighting | 20.0 | 90% | 18.0 |
| HVAC / air conditioning | 40.0 | 80% | 32.0 |
| Motors & pumps | 60.0 | 70% | 42.0 |
| Sockets / general purpose | 15.0 | 40% | 6.0 |
| Other / special loads | 10.0 | 60% | 6.0 |
| Subtotal (diversified) | 145.0 | 104.0 | |
| Demand load (× Ks 0.8) | 83.2 kW |
Result
| Demand kVA | 83.2 kW ÷ 0.85 = 97.9 kVA |
| Demand current | 97.9 kVA ÷ (√3 × 0.4 kV) = 141 A |
| Recommended transformer | 97.9 kVA ÷ 0.8 = 122 kVA → 160 kVA (load factor 61%) |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Distribution transformer (S13 oil-immersed) | 160 kVA · 10/0.4 kV · Dyn11 | 1 | POA |
| Low-voltage switchgear (GCK/GCS) | 98 kVA demand · 141 A | 1 | POA |
| Total equipment (transformer) | POA |
For electrical designers and consultants doing the first step of any distribution design — feeder, switchgear and transformer sizing from a load schedule.
Use the calculator
Worked example
A pre-computed reference example (crawlable — no JavaScript required). Enter your own parameters above for a live result.
Example 1 — office & light-industrial load schedule
Calculated demand load
83.2 kW
97.9 kVA at PF 0.85 · connected 145.0 kW · Ks 0.8
Overall demand factor
72%
Demand current
141 A
Transformer
160 kVA
Load factor
61%
Load schedule
| Load group | Connected kW | Demand factor | Demand kW |
|---|---|---|---|
| Lighting | 20.0 | 90% | 18.0 |
| HVAC / air conditioning | 40.0 | 80% | 32.0 |
| Motors & pumps | 60.0 | 70% | 42.0 |
| Sockets / general purpose | 15.0 | 40% | 6.0 |
| Other / special loads | 10.0 | 60% | 6.0 |
| Subtotal (diversified) | 145.0 | 104.0 | |
| Demand load (× Ks 0.8) | 83.2 kW |
Result
| Demand kVA | 83.2 kW ÷ 0.85 = 97.9 kVA |
| Demand current | 97.9 kVA ÷ (√3 × 0.4 kV) = 141 A |
| Recommended transformer | 97.9 kVA ÷ 0.8 = 122 kVA → 160 kVA (load factor 61%) |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Distribution transformer (S13 oil-immersed) | 160 kVA · 10/0.4 kV · Dyn11 | 1 | POA |
| Low-voltage switchgear (GCK/GCS) | 98 kVA demand · 141 A | 1 | POA |
| Total equipment (transformer) | POA |
Example 2 — commercial building with high HVAC share
Calculated demand load
134.6 kW
149.6 kVA at PF 0.9 · connected 235.0 kW · Ks 0.75
Overall demand factor
76%
Demand current
216 A
Transformer
200 kVA
Load factor
75%
Load schedule
| Load group | Connected kW | Demand factor | Demand kW |
|---|---|---|---|
| Lighting | 30.0 | 90% | 27.0 |
| HVAC / air conditioning | 120.0 | 85% | 102.0 |
| Motors & pumps | 40.0 | 60% | 24.0 |
| Sockets / general purpose | 25.0 | 50% | 12.5 |
| Other / special loads | 20.0 | 70% | 14.0 |
| Subtotal (diversified) | 235.0 | 179.5 | |
| Demand load (× Ks 0.75) | 134.6 kW |
Result
| Demand kVA | 134.6 kW ÷ 0.9 = 149.6 kVA |
| Demand current | 149.6 kVA ÷ (√3 × 0.4 kV) = 216 A |
| Recommended transformer | 149.6 kVA ÷ 0.8 = 187 kVA → 200 kVA (load factor 75%) |
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| Distribution transformer (S13 oil-immersed) | 200 kVA · 10/0.4 kV · Dyn11 | 1 | POA |
| Low-voltage switchgear (GCK/GCS) | 150 kVA demand · 216 A | 1 | POA |
| Total equipment (transformer) | POA |
How it was calculated
- · Connected load: P_conn = Σ P_i.
- · Diversified demand: P_d = Σ (P_i × Kd_i).
- · Calculated demand: P = P_d × Ks (simultaneity factor).
- · Demand apparent power: S = P ÷ PF; demand current: I = P ÷ (√3 · U).
- · Recommended transformer: S_tr = S ÷ target load factor (0.8), rounded up to a standard size.
Referenced standards
| Standard | Scope |
|---|---|
| IEC 60364 | Low-voltage electrical installations |
| IEEE 241 | Recommended practice for electric power systems in commercial buildings (Gray Book) |
| GB 50054 | Code for design of low-voltage electrical installations |
Frequently asked questions
What is the difference between connected load and demand load?
Connected load is the sum of all equipment nameplate ratings; demand load is the maximum power actually drawn simultaneously, equal to connected load x demand factor. A 500 kW connected load at 0.7 demand factor has a 350 kW demand. Transformers are sized to demand, not connected load. The calculator computes demand from connected load.
What demand factor should I use for different building types?
Typical demand factors: residential 0.3-0.5, commercial/office 0.4-0.6, industrial 0.6-0.8, continuous process 0.8-0.9. A hospital runs 0.7-0.8. Using the right factor prevents a 30-50% Transformer oversize. The calculator provides guidance and computes the recommended kVA.
How do I convert demand kW to transformer kVA?
kVA = demand kW / Power Factor. A 350 kW demand at 0.9 pf needs 389 kVA, so select 400 kVA. If power factor is uncorrected at 0.75, the same load needs 467 kVA — power factor correction shrinks the transformer. The calculator applies pf and selects the standard rating.
What is the NEC vs IEC demand factor difference?
NEC Article 220 gives table-based demand factors per appliance/load type; IEC/GB practice uses engineering judgment and experience factors per building type. Both aim to avoid oversizing. The calculator uses engineering demand factors aligned with GB 50052 and IEC practice.
How do I account for future growth in load demand?
Add 15-25% to the present demand for growth, then select the next standard transformer rating. If present demand is 350 kVA, plan for ~440 kVA and select 500 kVA (or 2x250 kVA). The calculator's margin guidance keeps the transformer loadable at 70-80% after growth.
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Results are engineering estimates for preliminary design and reference only. Always verify with the applicable standards, the equipment nameplate and a licensed engineer before procurement or installation.
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