TradeCalculator.co.uk
External Render Bead Calculator — Corner, Stop & Bellcast
Calculate corner bead, stop bead and bellcast bead quantities for external rendering. Includes fixing counts.
Height of render from bellcast to soffit
Number of external corners to bead
Where render stops at windows, doors etc.
Total horizontal length of bellcast bead
Default 3/m (300mm centres) — conservative. Renderplas/Weber dab adhesive at min 300mm vertical centres; bellcast at 300–700mm or a continuous adhesive bed.
Next up: related pages
How We Calculate This
This calculator works out the quantity of render beads needed for external rendering, based on wall dimensions, number of corners and stop ends.
The formula
- Corner beads: Number of corners × ceil(Wall height ÷ Bead length)
- Stop beads: Number of stops × ceil(Wall height ÷ Bead length)
- Bellcast bead: ceil(Total run length ÷ Bead length)
- Fixings: Total bead run length × Fixings per metre
Each corner and stop end is a separate vertical run, so the bead count is rounded up per arris— you cannot share one bead across two non-adjacent corners. A wall taller than a single bead simply takes two beads butted end-to-end. Bellcast is one continuous horizontal run along the base. All quantities round up to whole beads, as you cannot buy part-lengths. Fixings default to 3 per metre (300mm centres) — a conservative figure from Renderplas/Weber installation guidance. If you are pricing a full one-coat render job — bags, mesh and these beads together — use our monocouche render cost calculator.
Frequently Asked Questions
Render beads are metal or PVC profiles that provide clean, straight edges to external render. Corner beads protect and define external corners. Stop beads create a neat edge where render meets another material (windows, doors, different finishes). Bellcast beads sit at the base of render to throw water away from the wall.
A bellcast bead (or drip bead) is fitted at the bottom edge of external render, typically just above the DPC line. It has a small outward curve that directs rainwater away from the wall face, preventing staining and damp issues. Bellcast bead runs horizontally along the full width of the rendered area.
PVCu render beads are usually bedded on dabs of bead adhesive (or a continuous adhesive bed) at a minimum of 300mm vertical centres — roughly 3 dabs per metre, the default this calculator uses. They can also be fixed with stainless steel nails or screws on masonry. Bellcast beads are bedded on a continuous run of adhesive, or fixed every 300–700mm. Always use stainless steel or PVCu beads externally; galvanised steel can rust and is no longer accepted by NHBC/LABC for external render (Renderplas / Weber installation guidance).
Render beads are typically supplied in 2.5m lengths for PVCu beads (e.g. Renderplas, in packs of 25) and 3m lengths for stainless steel or galvanised metal beads. The 2.4m length sometimes quoted is an internal plasterboard/drywall bead matched to board height, not an external render length. For walls taller than the bead, butt beads end-to-end with a clean, straight joint (Renderplas, Tubeway Sales, Wickes).
Yes, corner beads are essential on all external corners. They provide a straight, plumb edge and protect the vulnerable corner from impact damage. Without corner beads, external corners will crack, chip and look untidy. Use austenitic stainless steel or PVCu beads suitable for external use — galvanised beads can rust and stain the render.
Was this calculator helpful?
Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.