How Many Piers Does Your Deck Need? Spacing & Layout Guide
A deck’s frame works like a bridge between two solid points. The joists carry the decking and everything on it, the beam carries the joists, and the posts carry the beam down into the piers. Every pier exists to shorten the unsupported distance the beam has to span on its own. Space piers too far apart and the beam bends more than it should, deflecting under load and stressing every connection above it. Space them too close and you have poured extra concrete and dug extra holes for no structural benefit. Pier spacing is really a question of how much span your beam can carry before it needs another point of support, and that number changes with beam size, species, and what the deck is holding up.
Quick answer
Most residential decks need a pier every 6 to 8 feet along each beam line, with a pier at each corner and additional posts at any beam splice. Doubled 2×10 beams commonly reach the upper end of that range; larger built-up or solid beams can stretch spacing toward 10 to 12 feet. Exact spacing depends on your beam size, wood species, and joist span, so treat this as a starting range, not a fixed rule.
Because that range shifts with your specific beam and joist setup, the fastest way to get an exact number for your project is to run it through the Concrete Pier Calculator, which factors in your deck dimensions and beam size instead of applying one blanket spacing to every deck.
What actually determines your pier spacing
Pier spacing is not one variable, it is the intersection of four. The first is beam size and species: a doubled 2×8 beam has less spanning capacity than a doubled 2×10, and Douglas fir carries load differently than Southern yellow pine. The second is joist span, since a beam supporting joists that run 12 feet is carrying more tributary load per foot than one supporting 8-foot joists. The third is design load, meaning whether the deck is a simple sitting area or needs to carry a hot tub, built-in seating, or a roof structure. The fourth is soil bearing capacity, which determines how much weight each individual pier footing can safely transfer into the ground without settling.
Change any one of those and the spacing that worked on your neighbor’s deck may not work on yours. This is why generic “piers every 8 feet” advice shows up so often online and why it is frequently wrong for a specific project.
Attached decks vs. freestanding decks: why pier count differs
A deck attached to the house with a ledger board is only carrying half the job on piers. The ledger side transfers its share of the load directly into the house’s existing foundation, so piers only need to support the beam line running parallel to and away from the house. A freestanding deck has no ledger to lean on, so every edge, including the side that would normally attach to the house, needs its own full run of properly spaced piers.
This distinction is a common source of confusion, and it is worth checking before you finalize a layout: a freestanding deck of the same footprint as an attached one will typically need one full additional beam line and its own set of piers, not just a few extra posts scattered around the perimeter.
Beam size and typical spacing between piers
The table below gives general starting ranges for common doubled dimensional beams under typical residential joist spans. Actual allowable spans vary by wood species, grade, and local code, so treat these as planning figures and confirm against your jurisdiction’s prescriptive span tables, such as those published by the American Wood Council, before finalizing a layout.
| Beam size | Typical spacing between posts |
|---|---|
| Doubled 2×8 | 5 to 6 ft |
| Doubled 2×10 | 6 to 8 ft |
| Doubled 2×12 | 8 to 9 ft |
| Tripled 2×10 | 9 to 10 ft |
| 6×6 or larger solid beam | 8 to 12 ft |
Notice the overlap between rows. A doubled 2×10 and a 6×6 solid beam can both land around 8 feet of spacing, which is exactly why picking a single number without knowing your beam size leads to guesswork rather than an engineered layout.
Pier diameter and depth: matching support to load
Spacing tells you how many piers you need, but diameter and depth tell you whether each pier can actually carry its share of the load. A widely used rule of thumb ties pier diameter to span: roughly 1 inch of diameter per foot of beam span, so a beam spanning 8 feet between posts commonly sits on 8-inch piers, and a 10-foot span moves up to 10-inch piers. This is a starting estimate rather than an engineered figure, and it should be adjusted upward for heavier loads or softer soil.
Pier depth is a separate question driven by your local frost line, not by beam span. In cold climates, piers need to extend below the frost depth set by local code to prevent frost heave from lifting the footing over winter; in warmer regions the minimum depth is usually driven by soil bearing requirements instead. Always confirm frost depth with your local building department, since it varies significantly by region and is not something to estimate from a national average.
Before you finalize your pier layout
- Confirm your beam size and speciesYour spanning capacity depends on both, and swapping either changes every spacing number downstream.
- Map your joist spanLonger joist spans increase the tributary load each pier carries, which can shrink your allowable spacing.
- Identify attached vs. freestandingFreestanding decks need a full beam line and pier run on the side a ledger would normally cover.
- Account for point loadsHot tubs, built-in benches, and pergola posts need dedicated piers placed under the load itself, not just along the standard spacing grid.
- Check local frost depth and soil bearingThese set your minimum pier depth and diameter and can override a spacing plan that looks fine on paper.
- Plan corner and splice piers firstEvery corner needs a pier, and every point where a beam is spliced into a longer run needs support directly under the joint.
Worked example: a 12×16 freestanding deck
Picture a simple 12-ft by 16-ft freestanding deck using a doubled rim joist as the beam along the 16-ft side. Start by placing a pier at each of the two corners, which already covers the two ends of that 16-ft run. That leaves 16 feet of beam to support in the middle. Dividing that distance into three equal sections gives spans of just over 5 feet each, which calls for two additional piers along the run, for four piers total on that beam line. The same process repeats for the opposite 16-ft beam line, since this is a freestanding deck with no ledger to rely on, bringing the project to eight piers before accounting for any point loads like a grill station or stair landing.
Run your exact numbers before you dig
Enter your deck length, width, and beam size to get a pier count, spacing, and diameter recommendation matched to your project instead of a generic rule of thumb.
Use the free Concrete Pier CalculatorMistakes with deck pier spacing
- Using one flat spacing number for every deck.An 8-foot rule that works for a doubled 2×10 beam will overstress a doubled 2×8 beam carrying the same joist span.
- Borrowing spacing rules from helical or steel pier systems.Screw pile spacing guidance (often 8 to 10 ft) is built around a different load path than poured concrete piers and should not be applied directly.
- Skipping piers under beam splices.A long beam built from shorter pieces needs a post directly under every joint, not just at evenly spaced intervals.
- Ignoring point loads.A hot tub or built-in bench concentrates weight in one area, and standard grid spacing alone will not support it without a dedicated pier.
- Guessing at frost depth instead of checking local code.An underspecified pier depth can lead to frost heave that shows up as a bouncing or uneven deck within a year or two.
- Treating an attached deck’s pier count as the template for a freestanding one.Freestanding decks need a full second beam line of piers where a ledger would normally carry the load.
5-step summary
- Confirm your beam size and species. This sets your maximum allowable span before you place a single pier.
- Determine attached or freestanding. This decides whether you need one or two full beam lines of piers.
- Place corner and splice piers. Corners and beam joints get support first, before you space out anything in between.
- Divide remaining spans to fit your beam’s capacity. Split the distance between fixed points until each section falls within your beam’s allowable span.
- Add piers for point loads and confirm diameter and depth. Adjust for heavy features, then size each pier to local frost depth and soil bearing.
Frequently asked questions
How many piers does a 12×16 deck need?
A typical 12-ft by 16-ft freestanding deck with doubled beam lines on the 16-ft sides needs roughly eight piers, four along each beam line, before accounting for point loads. An attached deck of the same size needs fewer, since the ledger side does not require its own piers.
What is the standard spacing for deck piers?
Most residential decks space piers 6 to 8 feet apart along the beam, though the exact figure depends on beam size, species, and joist span. Sources vary on the exact number, and it should be treated as a starting range rather than a fixed rule.
Do freestanding decks need more piers than attached decks?
Yes. An attached deck’s ledger board transfers part of the load into the house’s existing foundation, so only the beam line away from the house needs piers. A freestanding deck has no ledger, so it needs a full run of piers on both sides.
How deep should deck piers be?
Pier depth is set primarily by your local frost line, not by beam span. In cold climates piers need to extend below the frost depth set by local code, while in warmer regions depth is usually driven by soil bearing requirements. Check with your local building department for the exact figure in your area.
What size pier do I need for my deck?
A common starting rule is about 1 inch of pier diameter per foot of beam span, so an 8-foot span typically uses an 8-inch pier. This should be increased for heavier loads or softer soil conditions.
Can pier spacing be wider with a bigger beam?
Yes. Larger or built-up beams, such as a tripled 2×10 or a solid 6×6, can span further between posts than a doubled 2×8, which allows wider pier spacing for the same joist span and load.
How do I calculate pier spacing for a deck with a hot tub?
Start with your standard spacing plan based on beam size and joist span, then add dedicated piers directly under the hot tub’s footprint to handle the concentrated point load, rather than relying on the standard grid alone.
Is 8 feet too far apart for deck piers?
Not necessarily. Eight feet is within the typical range for a doubled 2×10 or larger beam under a moderate joist span, but it can be too wide for a smaller beam like a doubled 2×8 carrying the same load.
Get your exact pier count and spacing
The calculator returns pier count, spacing, and recommended diameter based on your deck’s actual dimensions and beam size.
Open the Concrete Pier Calculator