Maximum demand and diversity calculator
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Circuits | Cooker: type Cooker, or load 10.6 kW, cooker control unit has a socket Yes; Downstairs ring: type Sockets (ring or radial), rating or current 32 A, cooker control unit has a socket No; Upstairs ring: type Sockets (ring or radial), rating or current 32 A, cooker control unit has a socket No |
| Main fuse | 80 A |
| Supply voltage | 230 V |
Maximum demand: about 70.6 A after diversity (indicative)
- Within the guidance Maximum demand within the main fuse: 70.626 A UK-wide: IET On-Site Guide, Appendix A; BS 7671:2018+A4:2026 Reg 311.1. Check with the source
| Result | Value |
|---|---|
| Maximum demand after diversity (indicative) | 70.6 A |
| Connected load (no diversity) | 110.1 A |
| Headroom on the main fuse | 9.4 A |
| Circuit | Connected (A) | After diversity (A) | How |
|---|---|---|---|
| Cooker | 46.1 | 25.8 | 10.0 A + 30% of 36.1 A + 5 A for the socket |
| Downstairs ring | 32 | 32 | Largest of its type, in full |
| Upstairs ring | 32 | 12.8 | 40% of 32.0 A |
Show the working
- Cooker: 10.6 kW × 1000 ÷ 230 V = 46.1 A connected
- Downstairs ring: 32 A connected
- Upstairs ring: 32 A connected
- Cooker: 10.0 A + 30% of 36.1 A + 5 A for the socket = 25.8 A
- Downstairs ring: Largest of its type, in full = 32 A
- Upstairs ring: 40% of 32.0 A = 12.8 A
- Maximum demand after diversity: 70.6 A (connected 110.1 A)
- Headroom: 80 A main fuse − 70.6 A = 9.4 A
How it works
- Connected current per circuit = its rating, or load (W) ÷ supply voltage
- Cooker: the first 10 A in full + 30% of the rest + 5 A if the control unit has a socket (On-Site Guide Appendix A)
- Socket circuits: the largest in full + 40% of each additional socket circuit (On-Site Guide Appendix A)
- Circuits with no rule entered yet are counted in full (no diversity), which overstates the demand
- Headroom = main fuse − maximum demand after diversity
Diversity rules are from the IET On-Site Guide, Appendix A; our transcription is still being checked against the current edition.
Indicative only: an electrician or your network operator (DNO) confirms the maximum demand before you add a big load.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Supply voltage | 230 V | Our assumption Not yet checked against the source | Our choice: change it to suit your job UK nominal single-phase supply voltage (brief v2 E2). Researcher to cite the statutory source. |
Regulations and standards
- IET On-Site Guide, Appendix A (allowance for diversity, household installations)
- BS 7671:2018+A4:2026 Reg 311.1 (maximum demand)
Explained: The IET On-Site Guide, BS 7671 (the IET Wiring Regulations), Approved Document P (electrical safety).
The On-Site Guide and BS 7671 are used across the UK. Who may do the work differs: Part P applies in England and Wales; Scotland and Northern Ireland have their own rules.
| Table | Clause | Nations | Status |
|---|---|---|---|
| Diversity allowances for household installations | IET On-Site Guide, Appendix A (allowance for diversity, household installations); Researcher to transcribe each rule with its page reference | UK-wide | 3/8 values entered Not yet checked against the source |