About this calculator
This calculator derives socket count, switch count, and circuit count from a real list of what is actually in the room — not from floor area or a per-room-type guess. Draw the room's own shape, set its ceiling height, then add one entry per appliance or fixed point: a fridge, an oven, a hob, a dishwasher, a washing machine, a microwave, an extractor hood, a run of worktop sockets, a TV point, a desk/computer point, a general socket, or a light switch. Each entry sits on one of the room's own walls, at a real distance along it and a real mounting height — both shown on the drawing, not just listed as numbers.
Socket count does not follow from area. A 20m² kitchen and a 20m² bedroom need very different numbers of sockets, because they hold different things — which is exactly the defect an earlier version of this calculator had (it recommended 6 sockets for a 20m² kitchen, when a real kitchen needs one socket for each major appliance plus a worktop run, typically 12-16). This version fixes that by asking what is in the room instead of how big it is.
Formula
Every point you add contributes:
sockets contributed = 0 for a light switch
round(run length / 600mm), minimum 1, for a worktop run
1 for every other kind
switches contributed = 1 for a light switch, 0 otherwise
connected load (W) = powerDraw x sockets contributed, for a worktop run
(powerDraw is PER SOCKET the run resolves to)
powerDraw, for every other kind
socket count = sum of every point's own sockets contributed
switch count = sum of every point's own switches contributed
total load (W) = sum of every point's own connected load
circuit count = max(1, round_up(total load / 3680))
3680W is a 16A circuit at 230V — a common rating for a dedicated appliance/general-purpose circuit in many EU installations, not a code requirement. Circuit count is a straight division of total connected load by that figure, with no diversity/demand factor applied — a real design commonly derates simultaneous load (not everything runs at once, at full power, all the time); this calculator deliberately does not, to stay one plain, auditable number rather than adding a second guessed factor on top of the first. Treat the reported circuit count as an upper bound, not a final design figure.
A worktop run resolves to one socket roughly every 600mm of its own length — a common kitchen worktop socket spacing convention, not a standard — rounded to the nearest whole socket, minimum 1.
Every mounting height and power draw default (worktop 1100mm, general 300mm, switch 1200mm, and each appliance kind's own typical wattage) is a trade-practice/typical figure you can override per point — see the FAQ below for the exact list.
Worked example
A 20m² kitchen (5m x 4m), with:
fridge (300mm, 150W), oven (300mm, 2500W), dishwasher (300mm, 1500W),
hob (300mm, 3000W), extractor hood (2000mm, 200W),
microwave (1100mm, 1000W),
one 3.6m worktop run (1100mm, 100W per socket),
two light switches (1200mm, 100W each)
sockets: 6 single-appliance points + round(3600mm / 600mm) = 6 worktop sockets = 12
switches: 2
total load = 150 + 2500 + 1500 + 3000 + 200 + 1000 + (100 x 6) + (100 x 2)
= 150 + 2500 + 1500 + 3000 + 200 + 1000 + 600 + 200
= 9,150 W
circuits = round_up(9,150 / 3,680) = round_up(2.487) = 3
12 sockets, 2 switches, 3 circuits — and the height breakdown shows 4 sockets at 300mm (fridge, oven, dishwasher, hob), 7 at 1100mm (microwave plus the 6-socket worktop run), and 1 at 2000mm (the extractor hood).
FAQ
Why does each appliance have its own default mounting height and power draw instead of one shared set of numbers? Because they genuinely differ — a worktop appliance sits at worktop height (around 1100mm), a floor appliance near skirting height (around 300mm), and their typical power draws range from a fridge's ~150W to a hob's ~3000W. Every default is stated here so you can judge or override it:
| Kind | Default height | Default power |
|---|---|---|
| Fridge/freezer | 300mm | 150W |
| Oven | 300mm | 2500W |
| Hob | 300mm | 3000W |
| Dishwasher | 300mm | 1500W |
| Washing machine | 300mm | 2200W |
| Microwave | 1100mm | 1000W |
| Extractor hood | 2000mm | 200W |
| Worktop socket run | 1100mm | 100W per socket |
| TV point | 400mm | 150W |
| Desk/computer point | 300mm | 200W |
| General socket | 300mm | 100W |
| Light switch | 1200mm | 100W (the lighting it controls) |
A light switch doesn't draw power — why does it have a wattage? The figure stands for the typical lighting fixture load the switch controls, not the switch itself, so a lighting-heavy room still contributes to the circuit-count estimate. Override it per switch if your fixture's real wattage is known.
Why is the socket count grouped by mounting height instead of shown as one number? Because "how many sockets" is only half the useful answer for actually wiring the room — a trade also needs to know how many sit at each height, since sockets at the same height are often wired together on the same run.
Why doesn't circuit count apply a diversity factor? Because that would be a second guessed figure stacked on the first. A real design commonly assumes not every appliance draws its full rated power simultaneously and derates the total accordingly; this calculator sums every point's stated draw in full and divides by one stated circuit capacity, so the number stays a single, auditable calculation you can check by hand, not two compounded assumptions.
Why is total cable length not reported?
Because a real cable run needs an assumed starting point — a consumer
unit/distribution board position — which this calculator does not ask for
or model. Adding one just to produce a cable-length figure would mean
inventing an unrelated input nobody asked to be exact; see
cable-run-length (a separate calculator on this site) for that
calculation once you know your own run lengths.
What standard does this calculator cite?
None. Socket/switch placement, spacing conventions, and how many circuits a
given load implies are all practice-based electrician conventions that vary
by country — every figure this calculator uses is stated above so you can
judge it against your own jurisdiction's practice. meta.standards is
deliberately left empty.
Assumptions and limits
No standard is cited — see the FAQ above for the full list of default heights, power draws, worktop socket spacing, and the circuit capacity figure, all trade-practice/typical values, not code requirements. Circuit count is total connected load divided by one stated circuit capacity, with no diversity/demand factor — treat it as an upper bound. Total cable length is deliberately not reported (see the FAQ above for why). The plan drawing places every point at its own real wall position; each wall with at least one point also gets its own elevation view, with every point's own mounting height dimensioned individually.