TradeCalculator.co.uk
Timber Connector Calculator
Select joist hangers by timber size, framing anchors per connection, coach bolts and nail counts for timber-to-timber and timber-to-masonry joints.
Total joints of this type
Check manufacturer specification
For beam-to-post connections
Next up: related pages
How We Calculate This
This calculator selects the correct joist hanger model for your timber size and calculates the total connectors, nails, coach bolts and fixings needed for the specified number of connections.
The formula
Joist hangers = 1 per joist-to-wall/beam connection
Framing anchors = 1 per rafter/stud connection
Hanger nails = Hangers × Nails per hanger (8-12, every pre-punched hole)
Framing-anchor nails = Anchors × ~4-6 (every hole in the smaller clip)
Coach bolts = Connections × Bolts per joint (2-4)
The adjustable “Nails Per Hanger” input only drives the joist-hanger joints. Framing anchors and truss clips are smaller and have fewer pre-punched holes, so the calculator fixes them at 6 nails for rafter-to-plate and 4 for stud-to-plate. Beam-to-post uses coach bolts (plus a few coach screws on the post cap), not nails. Always fill every hole the manufacturer specifies.
Connector guide
- Joist hangers: joist-to-wall and joist-to-beam
- Framing anchors: rafter-to-plate, stud-to-plate
- Coach bolts: beam-to-post, heavy timber joints
- Always use specified fixings — never substitute
Working figures for this are collected in our UK Timber Connectors & Straps Guide reference table.
Frequently Asked Questions
Match the hanger width to the joist width. For a 47×200mm sawn joist use a 47mm-wide hanger — BAT 47/200, Expamet ST47 or Catnic JH47/200. 44mm hangers are for 44mm planed/regularised CLS (47×200 sawn finishes to roughly 44×195 planed), so don't try to seat a 47mm sawn joist in a narrower 44mm hanger. The hanger depth should match or be slightly less than the joist depth (hangers 150mm and deeper are made about 10mm short to allow for joist notching). Always check the manufacturer's load capacity tables against the actual loading.
A typical joist hanger needs 8-12 nails — usually 4-6 through the joist flange and 4-6 through the support flange. Use only the nails specified by the hanger manufacturer (typically 30mm or 35mm × 3.75mm galvanised nails). Never use screws unless specifically approved — screws can snap under shear loading.
Framing anchors (also called truss clips or twist straps) are used for: rafter-to-wall-plate connections (preventing wind uplift), stud-to-plate connections, and general timber-to-timber joints where a joist hanger is not appropriate. They are bent to suit the angle of the connection and nailed through pre-punched holes.
Common coach bolt sizes for structural timber connections: M10 for lighter brackets and pergola joints, M12 for medium loads (beam-to-post, decking posts), and M16 for heavy loads. Bolt length should be timber thickness + washer + nut + about 10mm. Pre-drill a clearance hole roughly 1–2mm larger than the bolt diameter (M12 → 13mm) so the shank passes through cleanly — the square neck under the dome head bites into the timber to stop the bolt rotating as you tighten. Drilling to the exact bolt diameter makes the bolt impossible to insert and risks splitting. Always use a washer under the nut (and under the head in soft timber) to prevent pull-through. Eurocode 5 (BS EN 1995-1-1) also specifies bolt holes at nominal diameter + 1mm.
No — standard wood screws must not be used in joist hangers. Screws are weaker in shear than nails and can snap under load. Only use the manufacturer's specified nails (or approved structural screws specifically rated for that hanger). Simpson Strong-Tie SD screws and similar structural screws are approved for some hanger models — check the data sheet.
Related Calculators
Was this calculator helpful?
Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.