MGP10 Bearer Spans and Floor Load Width Explained

Updated 2026-01-28 · MGP10 Span Tables

If joists are the floorboards' direct support, bearers are the next layer down — the members that gather up the joists and carry them to the posts or stumps. Their spans are dominated by one variable people often get wrong: floor load width. Here is how it all fits together.

The load path

Picture the load travelling downward:

1. The floor surface loads the joists.
2. The joists span across and load the bearers.
3. The bearers span across and load the posts or stumps.
4. Those carry down to footings.

Each member in that chain is sized from its own table. A bearer lookup is only valid once you know what the joists above are delivering to it.

Floor load width is the key input

Floor load width (FLW) is, broadly, how much floor a bearer has to carry — roughly half the joist span on each side of the bearer. It is the bearer equivalent of "how much weight is leaning on me."

• A larger FLW means more load on the bearer, reducing the span it can manage.
• A smaller FLW means less load, generally allowing a longer span or smaller section.

Bearer tables are organised around FLW, so measuring or calculating it correctly is essential. Misjudging FLW is one of the most common span-table mistakes.

Post spacing is a trade-off

Where you put the posts sets the bearer span. Spreading posts further apart gives a longer bearer span, which usually demands a deeper or higher-grade bearer; bringing them closer shortens the span and can let you use a smaller section. There is no free lunch — the span table prices the trade for you.

Single vs continuous

As with joists, a bearer continuous over several posts behaves differently from one spanning between just two, and the tables treat them separately. Read single vs continuous span so you choose the right column.

Approaching the lookup

To size an MGP10 bearer: establish the FLW it carries, set your post spacing (the bearer span), choose single or continuous, apply your wind class, then read the size that meets your span from the current table. The Span Spec Builder captures FLW and the rest so nothing is missed.

Keep going

Bearers carry joists, so revisit floor joist spans, and for roofs the same load-width thinking applies to rafters and roof members.

Frequently asked questions

Keep reading