How do I select the right joist hanger size?

Joist hangers must match the joist dimensions. For a 47×200mm joist, use a BAT 44/200 or equivalent (the 44mm width accommodates the 47mm joist with tolerance). The hanger depth should match or be slightly less than the joist depth. Always check the manufacturer's load capacity tables against the actual loading.

How many nails per joist hanger?

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.

When should I use framing anchors?

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.

What size coach bolts for timber connections?

Common coach bolt sizes for structural timber connections: M10 for light connections (stud-to-plate), M12 for medium loads (beam-to-post, pergola), and M16 for heavy loads. Bolt length should be timber thickness + washer + nut + 10mm. Always use a washer under the nut to prevent pull-through. Pre-drill the bolt hole to the exact bolt diameter.

Can I use screws instead of nails in joist hangers?

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.

TradeCalculator

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.

Joist/Timber Size

Determines hanger model

Connection Type

Type of joint

Number of Connections

Total joints of this type

Price Per Hanger (optional)

Price Per Framing Anchor (optional)

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
Nails = Connectors × Nails per connector (8-12)
Coach bolts = Connections × Bolts per joint (2-4)

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

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.