En-Suite Minimum Size Calculator — Feasibility Check

Using the most compact fittings (800mm quadrant shower, wall-hung toilet, cloakroom basin) the smallest workable footprint is roughly 1.9m x 1.1m (about 2.1 m²) with all three fittings along one wall, or about 0.9m x 1.9m as an L-shape down a longer wall. The three fittings cannot sit side by side in a run narrower than around 1.9m, so a 1.4m-wide wall only works in an L-shaped arrangement. For comfortable use, aim for 1.6m x 2.2m (about 3.5 m²). These figures follow the BS 6465-2 activity space of 600mm deep x 800mm wide in front of the WC and basin.

A 1.5m x 1.5m room (2.25 m²) comfortably holds two fittings: a shower and toilet, or a shower and basin, using compact fittings such as an 800mm quadrant shower and a wall-hung toilet. Fitting all three is not realistic in 1.5m x 1.5m even with the most compact products, because a side-by-side run of shower + toilet + basin needs about 1.9m of wall, and the L-shape alternative needs a wall about 1.9m long. For all three you really want a wall of at least 1.9m in one direction.

Wall-hung toilets save the most floor space with a projection of approximately 480mm from the wall versus 650mm for a close-coupled toilet. The cistern is concealed in a furniture unit or wall void. Back-to-wall toilets are a good middle ground at 500mm projection and do not require a concealed cistern frame. Both options create a more open floor area.

You generally do not need planning permission to add an en-suite within your existing property footprint. However, Building Regulations approval is required for drainage connections, ventilation (Approved Document F 2021 requires extract of 15 l/s intermittent or 8 l/s continuous for a room with a bath or shower; a WC-only room is 6 l/s), electrical work in a bathroom (Part P), and structural changes. You will need to notify your local Building Control or use a competent person scheme.

Sliding pocket doors or bi-fold doors are ideal for small en-suites as they do not swing into the room. A standard 762mm hinged door needs 762mm clear swing space inside the room. Pocket doors slide into the wall cavity and use zero floor space. There is a common myth that bathroom doors must open outwards — for a standard en-suite there is no Building Regulations requirement on swing direction, so an outward-opening hinged door is simply an optional space-saving choice. An outward-opening (or otherwise accessible) door is only required for accessible WCs under Approved Document M, such as the entrance-storey WC in a new dwelling and M4(2)/M4(3) accessible/adaptable homes.