The size of timber floor joists in Australia can vary depending on factors like span, spacing, load requirements, and timber species, building code and regulation. Common sizes of floor joists for residential applications are typically 140×42 mm, 190×42 mm, 240×42 mm, 290×42 mm, 140×65 mm, 190×65 mm, 240×65 mm, 290×65 mm.

The International Residential Code (IRC) specifies that the timber used for single span floor joists will typically be placed at 400 mm centers but no more than 600 mm centers. However, a 300 mm, 400 mm, 450 mm, 480 mm and 600 mm spacing are common for residential application. The common sizes of timber used for single span floor joists for different span include 140×42 mm, 190×42 mm, 240×42 mm, 290×42 mm, 140×65 mm, 190×65 mm, 240×65 mm, 290×65 mm.

All timber like different joists (floor joist, ceiling joist, pitched rafters, flat roof joist or rafters), wall plates, blocking, strutting, battens, firrings and nogging must be treated with preservatives to secure its durability.

In general, the single span floor joist is typically measured horizontally distance between two support end. The floor joists span may be either 2m, 2.5m, 3m, 3.5m, 4m, 5m and 6m and so on higher. In this article you know about what size timber or joists do i need for a specific span for floor that will help you in better understanding and to figure out or estimate of joist size and their depth according to span.

**Timber floor joist size australia- single span joists size and span**

As per Australian practices, the most common size of timber required for single span floor joists for residential applications are typically 140×42 mm, 190×42 mm, 240×42 mm, 290×42 mm, 140×65 mm, 190×65 mm, 240×65 mm, and 290×65 mm and the floor joists will typically be placed at standard 400 mm centers.

**Here are the single span joists size and their span as per Australian practices:-**

A 140×42 size of timber for single span joists can allow to span 3.2m @ 400c/c, 3.9m @ 300c/c, 3.1m @ 450c/c, 3.0m @ 480c/c, and 2.9m @ 600c/c.

A 190×42 size of timber for single span joists can allow to span 4.6m @ 400c/c, 5.0m @ 300c/c, 4.4m @ 450c/c, 4.3m @ 480c/c, and 4.1m @ 600c/c.

A 240×42 size of timber for single span joists can allow to span 5.5m @ 400c/c, 5.9m @ 300c/c, 5.3m @ 450c/c, 5.3m @ 480c/c, and 5.0m @ 600c/c.

A 290×42 size of timber for single span joists can allow to span 6.3m @ 400c/c, 6.8m @ 300c/c, 6.2m @ 450c/c, 6.1m @ 480c/c, and 5.7m @ 600c/c.

A 140×65 size of timber for single span joists can allow to span 3.9m @ 400c/c, 4.4m @ 300c/c, 3.6m @ 450c/c, 3.6m @ 480c/c, and 3.4m @ 600c/c.

A 190×65 size of timber for single span joists can allow to span 5.1m @ 400c/c, 5.5m @ 300c/c, 5.0m @ 450c/c, 4.9m @ 480c/c, and 4.6m @ 600c/c.

A 240×65 size of timber for single span joists can allow to span 6.1m @ 400c/c, 6.6m @ 300c/c, 6.0m @ 450c/c, 5.9m @ 480c/c, and 5.5m @ 600c/c.

A 290×65 size of timber for single span joists can allow to span 7.1m @ 400c/c, 7.6m @ 300c/c, 6.9m @ 450c/c, 6.8m @ 480c/c, and 6.4m @ 600c/c.

**Single span floor joist size for 3m span**

The size of timber required for single span floor joist for a 3m span need to be 140×42 @ 480c/c. This measure 42 mm wide by 140 mm deep. So, the size of the timber needed for single span floor joist to span 3m should be 140×42 @ 480c/c.

**Single span floor joist size for 3.5m span**

The size of timber required for single span floor joist for a 3.5m span need to be 140×65 @ 450c/c. This measure 65 mm wide by 140 mm deep. So, the size of the timber needed for single span floor joist to span 3.5m should be 140×65 @ 450c/c.

**Single span floor joist size for 4m span**

The size of timber required for single span floor joist for a 4m span need to be 190×42 @ 6000c/c. This measure 42 mm wide by 190 mm deep. So, the size of the timber needed for single span floor joist to span 4m should be 190×42 @ 600c/c.

**Single span floor joist size for 4.5m span**

The size of timber required for single span floor joist for a 4.5m span need to be 190×42 @ 400c/c. This measure 42 mm wide by 190 mm deep. So, the size of the timber needed for single span floor joist to span 4.5m should be 190×42 @ 400c/c.

**Single span floor joist size for 5m span**

The size of timber required for single span floor joist for a 5m span need to be 240×42 @ 600c/c. This measure 42 mm wide by 240 mm deep. So, the size of the timber needed for single span floor joist to span 5m should be 240×42 @ 600c/c.

**Single span floor joist size for 5.5m span**

The size of timber required for single span floor joist for a 5.5m span need to be 190×65 @ 400c/c. This measure 65 mm wide by 190 mm deep. So, the size of the timber needed for single span floor joist to span 5.5m should be 190×65 @ 400c/c.

**Single span floor joist size for 6m span**

The size of timber required for single span floor joist for a 6m span need to be 240×65 @ 450c/c. This measure 65 mm wide by 240 mm deep. So, the size of the timber needed for single span floor joist to span 6m should be 240×65 @ 450c/c.

**Single span floor joist size for 6.5m span**

The size of timber required for single span floor joist for a 6.5m span need to be 290×65 @ 6000c/c. This measure 65 mm wide by 290 mm deep. So, the size of the timber needed for single span floor joist to span 6.5m should be 290×65 @ 600c/c.

**Single span floor joist size for 7m span**

The size of timber required for single span floor joist for a 7m span need to be 290×65 @ 400c/c. This measure 65 mm wide by 290 mm deep. So, the size of the timber needed for single span floor joist to span 7m should be 290×65 @ 400c/c.

**Conclusions:-**

As per Australian practices, the most common size of timber required for single span floor joists for residential applications are typically 140×42 mm, 190×42 mm, 240×42 mm, 290×42 mm, 140×65 mm, 190×65 mm, 240×65 mm, and 290×65 mm and the floor joists will typically be placed at standard 400 mm centers.