What is a data centre? How big they are and how much power they use
A plain-English definition, the only government capacity estimate, how PUE turns IT load into grid demand, and what Tier III and IV mean.
A data centre is a building, or part of one, that houses the servers, storage and network equipment an organisation or its customers run, together with the power and cooling that keep them running. In the UK they range from a single room of racks to campuses planned at hundreds of megawatts. The only government estimate of capacity, from the Department for Science, Innovation and Technology (DSIT), puts colocation data centres in Great Britain at 1.6 GW of IT power as at autumn 2024 (DSIT, published 1 May 2025). That is the maximum rated IT load, not what the buildings draw from the grid.
What kinds of data centre are there?
DSIT separates two types in its estimate. Colocation data centres are those where several organisations rent space for their own servers. Enterprise data centres are run by a business for its own use, and DSIT's figure leaves them out. Two further terms are in everyday use. A hyperscale data centre is a very large facility built for one cloud or platform operator. An edge data centre is a small site close to users or to a telecoms network. We have not found an official UK size threshold for any of the four, so quote the source's own definition whenever you use a number. Our guides to colocation, hyperscale and edge sites give the solar view of each.
How big is a data centre?
Size is measured in megawatts (MW) of IT load: the electrical power the computing equipment is rated to draw. DSIT's 1.6 GW is spread very unevenly: London 1,048 MW, Wales 154 MW, the South East 128 MW, the South West 53 MW, the North West 52 MW, the East 44 MW and Scotland 30 MW. DSIT does not state a number of facilities or an average site size, so no official figure exists for a typical UK data centre. The UK data centre map shows the regional table and the clusters behind it.
At the top end, scale is set by plans rather than buildings. Government says DataVita plans more than 500 MW of on-site power at its Airdrie site within four years (GOV.UK, Lanarkshire AI Growth Zone); that single plan is about a third of the whole 1.6 GW DSIT estimate. In the North East, government says the AI Growth Zone, including the new Blyth data centre, will raise capacity to 1.1 GW within six years (GOV.UK). These are stated plans, not connected capacity; the AI Growth Zones page lists all five.
How much power does a data centre use?
A data centre's grid demand is its IT load plus everything needed to support it: cooling, power conversion and lighting. Power usage effectiveness (PUE) expresses that overhead as a ratio of total data centre energy to IT energy, and ISO/IEC 30134-2 is the standard that defines how to measure it (ISO/IEC 30134-2 record). A PUE of 1.5 means each kWh of IT use brings 0.5 kWh of overhead. Our data centre PUE page explains the measurement points and what the ratio does not tell you.
Because the load is continuous, an annual figure follows from the rating: 1 MW of IT load running all year at a PUE of 1.5 is 1.5 MW of facility demand, or about 13,140 MWh a year (1.5 MW × 8,760 hours). That is arithmetic from the definition, not a measured UK average.
Why do data centres use so much electricity?
Servers, storage and network equipment run around the clock, and almost every watt they draw leaves the building as heat that cooling has to remove. Demand is also expected to grow. In 2022 the electricity system operator, expecting significant capacity growth, noted that no central authority in Great Britain was monitoring the data centre landscape (ESO briefing ahead of Future Energy Scenarios 2022); the government capacity estimate above was published in 2025. For why published counts disagree, see why UK data centre capacity estimates disagree.
What does a Tier III or Tier IV data centre mean?
Tier ratings come from Uptime Institute (Uptime Institute Tier classifications). Tier I has basic capacity. Tier II adds redundant capacity components. Tier III is concurrently maintainable, so any component can be taken out for maintenance without affecting IT. Tier IV is fault tolerant, with independent, physically isolated systems. Uptime says it is the only firm licensed to certify a Tier, so ask for the certificate when a site claims one. Our Tier III/IV resilience page covers what that means for work on the roof.
What is the biggest issue for UK data centres?
There is no single answer, but in London and the South East it is the grid connection. The analysis we summarise in West London data centre grid limits sets out why connection timelines, not land, now shape where capacity can be built there.
Where solar fits
A data centre's flat, continuous load means a rooftop array's output is used on site, but a roof covers only a small share of a facility's demand. What it saves depends on the roof, the tariff and the installed cost; see data centre solar cost and how a system is designed. This site is a publisher, not an installer. If you have a question about a source on this page, email dc@seodons.co.uk and we reply by email.
Frequently asked questions
What is a data centre?
A data centre is a building, or part of one, that houses servers, storage and network equipment with the power and cooling to keep them running. DSIT distinguishes colocation sites, where several organisations rent space, from enterprise sites run by one business.
How large is a data centre?
There is no official typical size. Size is quoted in MW of IT load. DSIT estimates 1.6 GW of colocation IT power across Great Britain as at autumn 2024, with London holding 1,048 MW of it, and publishes no facility count or average.
How much power does a data centre use?
It depends on the site. Grid demand is the IT load multiplied by the PUE: at a PUE of 1.5, 1 MW of IT load means 1.5 MW of facility demand, or about 13,140 MWh over a year.
What is the biggest issue with data centres in the UK?
There is no single answer. In London and the South East it is the grid connection: our West London analysis sets out why connection timelines, not land, shape where capacity can be built there.
What is a Tier III data centre?
Tier III is Uptime Institute's concurrently maintainable level: any component can be shut down for maintenance or replacement without affecting IT operations. Uptime says it is the only firm licensed to certify a Tier.
Working on solar for a data centre roof?
Four short steps. This site is a publisher, not an installer. We read every enquiry and reply by email.