Page and reference sources last reviewed 27 July 2026. Manufacturer documents can be revised or withdrawn — always confirm the current linked publication before final selection.

Australian floor load width tool

Floor Load Width Calculator Australia

Estimate preliminary floor load width for a simple deck or residential floor bearer, then use the diagrams and examples below to identify the correct FLW column in a source span table.

Open calculator Read the FLW guide

FLWFloor load width describes the tributary width of deck or floor area carried by a bearer. It is not the bearer span.

Estimate preliminary floor load width

Bearer positionJoist span / tributary width side A (mm)Joist span / tributary width side B (mm)Round to common published column

Use this as a starting point for understanding load width. Complex layouts, cantilevers, stairs, roof loads, point loads and concentrated loads need separate review.

Estimated floor load width

1200 mm

For an edge bearer, preliminary FLW is half the joist span loading from one side.

FLW definition

What is floor load width?

Floor load width, commonly abbreviated to FLW, is the tributary width of deck or floor area assumed to load a bearer or beam. It converts an area load into the line of load carried by that member for a span-table check.

Edge bearer

An edge bearer receives joist load from one side. For a simple supported layout, a preliminary FLW is commonly half of the joist span feeding that bearer.

Internal bearer

An internal bearer receives joist load from both sides. A preliminary FLW commonly adds half the supported joist span from each side.

Simple geometry only: Cantilevers, verandah roofs, stairs, openings, point loads, concentrated loads and irregular support layouts can require different tributary-width formulas.

Worked diagrams

Identify the floor area that contributes load to the bearer

Edge bearer with a 2400 millimetre joist span and a highlighted preliminary floor load width of 1200 millimetres. — Simple edge bearer: half of the supported joist span contributes to the bearer from the loaded side.

Internal bearer loaded from both sides with half of a 2400 millimetre span and half of a 3000 millimetre span highlighted for a total FLW of 2700 millimetres. — Simple internal bearer: add the tributary contribution from side A and side B.

Worked examples

Preliminary edge and internal bearer calculations

Edge bearer example

Supported joist span: 2400 mm

FLW = 2400 ÷ 2 = 1200 mm

Start with the 1200 mm source-table column where that table uses the simple half-span method.

Internal bearer example

Side A span: 2400 mm; side B span: 3000 mm

FLW = 1200 + 1500 = 2700 mm

If the table has no 2700 mm column, the next higher published column is commonly used for a conservative preliminary check unless the source says otherwise.

Using a span table

FLW selects the load-width column; bearer span selects the allowable support spacing

Term	Meaning	Where it is used
Floor load width	The tributary width of floor or deck area carried by the bearer.	Selects the applicable FLW or supported-joist-span column in the bearer table.
Bearer span	The distance the bearer spans between posts, piers, walls or other supports.	Compared with the maximum bearer span shown for the selected product and FLW column.
Post spacing	The setout distance between repeated bearer supports.	Often establishes bearer span in a simple layout, but end supports, cantilevers and unequal bays must be checked.
Joist span	The distance joists span between bearers or other joist supports.	Used to determine tributary load contribution and to check the joists themselves.

Calculation pathway

Use FLW as one step in the bearer check

1. Draw the supports

Mark joists, bearers, walls, posts, cantilevers and any openings or concentrated loads.

2. Find tributary width

Identify the portion of floor or deck area delivering load to the bearer.

3. Select the source column

Use the exact or next applicable conservative FLW column according to the source instructions.

4. Check bearer span

Compare the required support-to-support span with the product value and verify all source notes.

Reference sources

Australian source documents that explain floor load width

The calculator applies simple tributary-width geometry. The linked manufacturer documents illustrate how FLW or supported joist span is used in actual product tables and why more complex layouts need source-specific formulas.

Source	Document/version	Relevant use
Spantec — Boxspan	Boxspan Residential Span Tables — April 2019	Definitions and floor load width diagrams, including source-specific formulas for layouts more complex than the simple calculator.
Meyer Timber — meyPINE3	meyPINE3 Handy Span Guide — updated March 2024	Defines load width and provides floor-bearer tables arranged by FLW.
Hyne Timber	Hyne common product span tables	Provides floor-bearer and deck-bearer source tables for checking the selected load-width condition.

Scope of this calculator

Edge mode divides the entered supported joist span by two. Internal mode adds half of each entered supported joist span. Custom mode adds tributary widths already determined by the user. Rounding is optional and only assists with preliminary selection of a common table column.

Floor load width FAQs

Common questions about FLW, bearer span and post spacing

What does FLW mean in a bearer span table?

FLW means floor load width. It is the tributary width of deck or floor area assumed to load a bearer or beam for the applicable source-table check.

How do I calculate FLW for a simple edge bearer?

For a simple edge bearer carrying joists from one side, a common preliminary starting point is half of the supported joist span. Confirm the source document because cantilevers, verandahs and irregular load paths can use different rules.

How do I calculate FLW for a simple internal bearer?

For a simple internal bearer, add the tributary contribution from each side—commonly half of the supported joist span on side A plus half of the supported joist span on side B.

Is FLW the same as bearer span or post spacing?

No. FLW is the width of floor area loading the bearer. Bearer span is the distance between bearer supports, which may correspond to post or pier spacing in a simple layout.

Is floor load width the same as the full deck or floor width?

Not necessarily. FLW follows the tributary area carried by the member and depends on the framing support layout.

Should I round FLW up to the next source-table column?

For a preliminary comparison, selecting the next higher published FLW column is commonly conservative when the exact value falls between columns, unless the source gives a different method.

Can the FLW calculator handle cantilevers, stairs or point loads?

No. The simple calculator does not resolve complex cantilevers, openings, stairs, point loads, concentrated loads or non-uniform support layouts. Those cases require source-specific calculation or engineering review.

Can this FLW calculator be used for final design?

No. It is a preliminary geometry and table-navigation aid. Final selection must use the current source document and account for the complete project load path and design requirements.

Next step

Important: This calculator does not determine structural capacity and does not account for all possible load paths. Use it to understand preliminary FLW only, then verify the current manufacturer table and obtain project-specific engineering where required.