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Vanity Unit Sizing Calculator — Basin, Clearance & Storage
Calculate vanity unit sizes with basin clearance, plumbing offsets and storage capacity.
Measure the wall space for the unit
400mm cloakroom, 500mm standard
Negative = left, positive = right
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How We Calculate This
This calculator recommends the best vanity unit size based on your available wall space, basin type, bathroom type and plumbing requirements.
How it works
- Width matching: Finds the largest standard UK unit size that fits your available wall space
- Basin clearance: Ensures sufficient width for the selected basin type and count
- Plumbing check: Verifies depth and offset clearances for waste and supply pipes
- Storage volume: Calculates usable internal volume accounting for carcass thickness and plumbing zone
- Configuration: Suggests door and drawer counts based on unit width and selected style
Standard UK vanity units range from 400mm cloakroom widths to 1200–1800mm double-basin units. The sizes, carcass thicknesses and basin cut-out dimensions used here follow common UK manufacturer conventions (suppliers such as Roper Rhodes, Burlington, Britton and Hudson Reed) — they are typical averages, not a British Standard. Cut-out sizes in particular vary by model, so always confirm the figure against your basin’s published cut-out template before cutting the worktop.
Frequently Asked Questions
Common UK vanity unit widths are 400mm (cloakroom), 500mm (compact), 600mm (standard single basin), 750-800mm (wider single), 900mm (generous single or narrow double), and 1200mm (double basin). Depths typically range from 400mm (cloakroom) to 500-600mm (standard). Heights are usually 800-850mm including the worktop, matching standard basin mounting height.
For a cloakroom, a 400mm deep vanity unit is usually sufficient and helps maximise floor space in a small room. Slimline units as narrow as 350mm depth are available but may require a compact bottle trap and careful plumbing. Standard 500mm depth units work well in cloakrooms that are at least 1.2m wide, giving more worktop space and storage.
Allow at least 80mm behind the back panel for waste pipes (32mm) and hot/cold supply pipes (15mm). Most vanity units have a pre-cut or removable back panel to accommodate plumbing. If the waste pipe exits from the wall rather than the floor, ensure the unit back panel can be cut without compromising structural integrity. Push-fit connections are recommended for accessibility.
A 900mm vanity unit can technically accommodate two small basins, but it is tight. Each basin typically needs at least 400mm width plus a 100-200mm gap between them. For comfortable use, a 1200mm or wider unit is recommended for double basins. Many UK manufacturers offer purpose-built double basin units in 1200mm and 1500mm widths.
Drawers offer better access and organisation for bathroom storage, as you can see all contents without bending down. However, drawers must be cut around waste pipes, which reduces usable depth in the top drawer. A popular configuration is two drawers below with a false drawer front at the top (behind the basin). Doors are simpler for plumbing access but less organised. Soft-close mechanisms are recommended for both.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.