Electrical Installation Cost Calculator UK

How the calculation works

Electrical installation cost in the UK: what drives the estimate?

The electrical installation is one of the least visible parts of a building project, and for that reason it is often underestimated. Once the plaster is closed, cable routes cannot be checked without opening the walls again, so a vague quote is easy to accept and hard to challenge later. This calculator makes the main variables explicit so that quotes from different electricians can be compared on the same basis.

The calculator builds its estimate from four inputs: the floor area of the home, the type of installation, the quality of the components and the region. It adds a fixed allowance for the consumer unit and the electrical installation certificate, and an optional allowance for a three-phase supply. The result is an indicative figure for budgeting. It is not a fixed price and does not replace a survey of the property.

Type of installation: the decision with the largest effect

The type of work has the greatest influence on the total, because it determines how much labour and making good is involved.

A new build means the walls and floors are open during construction. Cables are run directly through the structure, with no chasing and no reinstatement of finished surfaces. It is the least expensive option per square metre, and a detached house of 120 m² is a typical case for this scenario.

A partial rewire replaces the consumer unit and the main circuits, and keeps existing cabling that is sound. It suits a home where the cabling is PVC-insulated and in good condition, but the consumer unit is old, lacks RCD protection or cannot take new circuits. The cost per square metre is moderate.

A full rewire replaces all the cabling. Chases are cut into the plaster, new cable or conduit is installed, and the walls are made good before decoration. It is the most expensive option per square metre, but it gives the most complete result. It is the usual route where a condition report finds that existing rubber-insulated or lead-sheathed wiring has deteriorated, because the insulation of these materials wears with age. Its condition is established by inspection under BS 7671, not by the material alone. It is also the usual choice where the wiring has been altered in ways that cannot be documented.

Take a semi-detached house in Manchester with 90 m² of floor area. If the cabling is sound, the partial rewire option gives a realistic budget. If the cabling is rubber-insulated, the full rewire figure is the one to plan around, and the difference between the two should inform whether the wiring is replaced at the same time as other building works.

Cost components

• Type of installation: the largest variable, as explained above.
• Floor area: the total of all rooms, including hallways, landings and any loft or cellar that is wired.
• Material quality: the basic option meets BS 7671 with basic components. The standard option uses mainstream components. The premium option adds higher-end components and networked controls such as smart lighting and home automation.
• Region: electricians' labour rates vary across the UK. The calculator applies a regional factor, and higher factors apply in regions where rates are usually higher, such as London and the South East.
• Consumer unit and certificate: a fixed allowance covering the enclosure, miniature circuit breakers, RCDs and the installation certificate.
• Three-phase supply: only where needed. The connection is arranged with the local distribution network operator, which may require a supply upgrade and new metering.

How the formula works

The formula is C = (A × P + CU) × f_q × f_r + T × f_r. The expression works in three steps. First, the floor area A is multiplied by the base rate P for the chosen type of work, and the fixed allowance CU for the consumer unit and certificate is added. Second, this sum is multiplied by the material quality factor f_q and the regional factor f_r. Third, the three-phase allowance T, where it applies, is multiplied by the regional factor f_r and added to the result.

Two structural points matter when reading the result. The quality factor applies to the main installation and the consumer unit, but not to the three-phase allowance. The regional factor applies to both the main installation and the three-phase allowance. Because the fixed allowance does not scale with area, the total does not double when the floor area doubles. For an 80 m² home and a 160 m² home with the same options, the total for the larger home is less than twice the total for the smaller one.

Edge cases

• With no three-phase supply, T is zero and the last term disappears.
• The premium quality factor raises the consumer unit allowance as well as the installation, because the factor multiplies the whole bracket.
• In very small homes, the fixed allowance makes up a larger share of the total, so the cost per square metre looks higher than in a larger home.
• Changing the region changes only the regional factor. It does not reflect local differences in the supply connection beyond the three-phase allowance.

When to use this calculator

Use it at an early stage, before a survey, to set a realistic budget range. It is also useful for comparing a new build, a partial rewire and a full rewire for the same home, and for checking whether an itemised quote is broadly in line with the market. It is most valuable when walls are about to be opened for another project, because it prompts you to coordinate the electrical work at the same time.

When not to use it

Do not rely on it for commercial premises, where different requirements and inspection regimes apply. Listed and heritage buildings may need consent for alterations and specialist methods of making good, which the calculator does not reflect. It is not a tool for fault finding or for choosing the size of a single circuit. Those tasks need the design and testing carried out by a qualified person. Solar generation, battery storage and high-power charging beyond the three-phase allowance have their own requirements and are not covered.

The estimate applies across the UK, but the certification route differs between England and Wales, Scotland and Northern Ireland, so confirm the rules for your nation.

Standards and regulations

BS 7671 is the national wiring standard for electrical installations in the UK. It sets out how circuits are designed, protected and verified, and several of its requirements shape the cost directly.

Circuits must be designed for their load and protected by a suitable device. In practice, most homes have separate lighting and socket circuits, with dedicated circuits for the cooker, the shower, the immersion heater and, where planned, an electric vehicle charger.

BS 7671 requires RCD protection with a rated residual operating current of 30 mA for socket outlet circuits up to 32 A. Cable size must suit the protective device. Ring final socket circuits protected by a 32 A device commonly use 2.5 mm² cable, and lighting circuits protected by a 6 A device commonly use 1.5 mm² cable. Using cable smaller than the protective device requires is a breach of the standard and a fire risk, so any quote that relies on undersized cable to reduce material cost should be questioned.

Miniature circuit breakers used in UK installations are standardised to BS EN 60898.

Part P of the Building Regulations applies in England and Wales. Most new circuits, consumer unit replacements and rewires are notifiable work under Part P. Notifiable work must either be notified to building control in advance or be carried out by an electrician registered with a government-approved competent person scheme, which then certifies it. Scotland and Northern Ireland have their own building standards systems, and the route to certification differs.

An electrical installation certificate confirms that new work complies with BS 7671. An electrical installation condition report assesses the condition of an existing installation. Private landlords in England must have the fixed wiring inspected by a qualified person at least every five years, under the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020.

Home insurance policies may set conditions about electrical work, and a claim for electrical damage can be disputed if the work was not carried out or certified properly. Check the policy wording before the work starts.

Common mistakes

The first mistake is accepting a fixed-price quote that is not itemised. A proper schedule lists the circuits, cable sizes, the consumer unit and its protective devices, the making good and the certificate. Without these items, the scope cannot be compared and extras tend to appear later.

The second is starting work without a design. For a full rewire or a consumer unit replacement, a written design or schedule of works from a competent person protects the homeowner. Without it, an electrician may choose solutions that pass a visual check but do not match the real load of the home. A badly sized installation trips the consumer unit whenever several high-load appliances run together, which is a common complaint in older homes.

The third is closing the walls before the other cabling has been coordinated. Network cables, aerial and satellite feeds, smart home sensors and CCTV cables must be routed before the plaster goes back on. Opening the walls later means cutting new chases, making good and redecorating, which costs far more than the cable itself.

The fourth is choosing on price alone. The cheapest quote may rely on undersized cable, omit the certificate or exclude the making good. Compare quotes on the same scope before comparing totals.

When to hire a professional

Electrical installation work in a home should be carried out by a competent electrician, and most significant work must be certified. Ask for proof of the electrician's registration with a competent person scheme or the local authority notification, and check that registration on the scheme's public register before agreeing a price.

For a rewire, a consumer unit replacement or a new supply, ask for a design or schedule of works, the certificate on completion and a written statement of what is included and excluded. These documents are also what buyers, surveyors and tenants ask for when a home is sold or let.

Ofgem regulates the energy networks in Great Britain. Changes to the supply, including a three-phase connection, are arranged with the local distribution network operator, which should confirm the requirement and any associated work in writing before anything is planned.

The calculator gives a starting point. The design, the quote and the certificate come from a qualified professional.