Here’s a ready-to-paste HTML article that compares basement support post sizes using load, height, and rated capacity. It includes a spec table, guidance on code minimums and permanent-use rules, plus an FAQ section.
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Pick a basement support post by matching the load it carries and its installed height to a rated capacity, not by picking a 4×4 or 6×6 on sight.
Three numbers settle basement support post size: the load the post carries, the unsupported height, and the manufacturer’s listed capacity at that exact height. Line those up and the labels — 4×4, 6×6, 3-inch pipe — fall in behind them.
What Size Support Post Does A Basement Need?
For permanent basement support, the size that matters is the listed capacity at the height you need, not the lumber dimension on the label. Code text sets a floor rather than a ceiling: wood columns no less than 4 inches by 4 inches, steel columns no less than 3-inch-diameter standard pipe or an approved equivalent.
Judge posts by what they hold at a given height, and the spread shows up fast. Every range and capacity below comes from a current product listing or spec sheet.
| Product | Adjustable Range | Rated Capacity |
|---|---|---|
| Akron 34-in Adjustable Jack Post | 34–55 in | 18,000 lb compressed; 14,000 lb at maximum height |
| Peak Adjustable Steel Jack Post | 31–55 in | 8,090 lb (36 kN) |
| Peak Adjustable Steel Jack Post | 54–100 in | 8,090 lb (36 kN) |
| Tiger Jack Post 5007295 | Up to 24 in | 24,700 lb at full extension |
| VEVOR floor jack | 12–16 in | 9,700 lb; 4 x 6 in plates |
| McMaster-Carr support post | 24 in | 18,000 lb |
| McMaster-Carr support post | 41–64 in | 17,000 lb |
| McMaster-Carr support post | 100 in | 14,000 lb |
Height and capacity are printed as separate columns because they belong together.
The minimums people quote most often trace back to older IRC text, where the IRC’s minimum column sizes set wood at 4×4 and steel at 3-inch pipe, and where columns must be restrained against lateral displacement at the bottom end. Those are minimums for the smallest post the code allows, not a rating for the post in your basement.
Basement Support Post Sizing: Why Height Changes The Rating
A taller setting almost always means a lower rating, because a longer unsupported length bends under the same load.
Capacity isn’t the only ceiling. Your basement has to clear those limits before the post’s own rating comes into play.
Low clearances change the pick too. The adjustable range narrows the field first; the load rating at that height picks the winner.
Comparing listings one at a time gets old fast. Our tested roundup of basement support posts lines up rated heights and capacities so you can start from the load instead of the price tag.
Permanent Posts, Code Minimums, And Common Mistakes
Permanent basement support calls for a product certified for structural use, not a temporary jack. Industry guidance for permanent support posts notes that they are typically hollow with a 3-inch minimum diameter, and that temporary support posts are not meant for permanent use.
Bottle jacks and foundation jacks sold for short-term shoring end up under beams permanently all the time. One marketplace listing claims a foundation jack can serve permanently as secondary support — a seller’s claim, not a code approval.
