For a standard wood guard with 4x4 posts, plan on posts no more than 6 feet apart, measured center to center. Larger 6x6 posts are commonly allowed to go further, and cable railings need posts much closer together, around 4 feet. The catch is that the model residential code does not hand you one universal number, so the figure that counts is the one your local building department and your railing system’s installation instructions accept.
Below, we cover the common limits, where they come from, how to measure correctly, and what changes with cable and metal railings. We build decks and railings in Everett, WA, so we also cover what Everett expects on your plans.
TL;DR
- Wood guards with 4x4 posts: keep posts at 6 feet on center or less. Posts 8 feet apart is a limit local guides tie to heavier post and rail setups.
- Cable railing is tighter: Grafton, Massachusetts, specifies posts no more than 4 feet on center and cables no more than 3 inches apart.
- Always measure on center (middle of one post to the middle of the next), not the gap between posts.
- Everett requires deck plans to show guard height, post spacing and picket spacing, so decide spacing before you apply for a permit.
- A railing is only as strong as its post connections. Spacing and attachment work together.
Table of Contents
- What the code says about post spacing
- Maximum spacing by post type and material
- How to measure post spacing correctly
- Spacing and openings work together
- Post connections matter as much as spacing
- What Everett, Washington expects
- Common spacing mistakes
- Perspective
- Want a railing laid out right the first time?
- FAQ
- Sources
What the code says about post spacing
Most homeowners expect a single line in the building code: “posts shall be X feet apart.” It is not that simple. The residential code concentrates on where guards are required, how tall they must be, how large an opening can be, and how much load the guard must carry. In many jurisdictions a guard is required where the walking surface is more than 30 inches above grade, and openings must stop a 4-inch sphere from passing through, according to a deck railing calculator reference. Heights are typically 36 inches for homes, and some places require 42.
Post spacing then falls out of the strength requirement. Minnesota’s code, as explained by the City of Grand Rapids, calls for guards to resist a 200-pound horizontal load. Whether a given post size, rail and spacing can do that is what building departments check, and they publish prescriptive deck guides so you don’t have to hire an engineer for a standard design.
That is why you see slightly different numbers in different places. Here is what several official deck guides say:
| Source | Post and spacing detail |
|---|---|
| City of Chesapeake, VA | 4x4 posts at 6 feet maximum, 4-inch sphere rule for balusters, hold-down anchors rated at least 1,800 pounds |
| Transylvania County, NC | Rail posts not more than 8 feet on center, bolted with 2-3/8-inch galvanized bolts, nut and washer, pickets 4 inches maximum apart |
| Livonia, MI | Guard posts 4x4 minimum, no notching, hold-down anchors of at least 1,800 pounds installed to manufacturer instructions |
| Grafton, MA | Cable railing: 3-inch maximum cable spacing, posts no more than 4 feet on center |
The practical read: 6 feet is the number you will see most for 4x4 wood posts, and 8 feet shows up where the post or rail is beefier. When a guide gives you a range, design to the tighter figure. A railing built at 5 feet 6 inches is easy to approve and feels stiffer underhand than one stretched to the limit.
Maximum spacing by post type and material
Wood posts
A 4x4 post at 6 feet on center is the standard recipe in the official guides above. Heavier posts, such as 6x6, are commonly allowed wider spans, up to about 8 feet on center according to DecksDirect’s spacing guide, but that is a general figure. Check your local guide before drawing it into your plan.
The rail matters too. A thin or unsupported top rail flexes between posts, and a deck full of guests leaning on it is the real test. If you plan to spend time at the rail with a drink in hand, favor a stiffer rail and shorter spans.
Composite, aluminum and other manufactured systems
Manufactured railing kits come with their own tested spans, and an inspector will usually accept the manufacturer’s installation instructions as long as the system is rated for guard use. One aluminum railing manufacturer’s installation page states that when its railing serves as a guardrail, post center to center spacing must not exceed 96 inches for picket panels or 75 inches for glass, because going further is outside its engineering specification and could fail inspection.
Two things follow. First, the maximum differs between product lines, so you cannot swap one brand’s panel into another’s post layout. Second, the panel length on the box is your spacing. Plan the posts around the panel size, not the other way around.
Cable railing
Cable infill is flexible, so you manage two separate problems: how far apart the structural posts are, and how much the cables deflect between them. Grafton’s deck guide, revised March 4, 2025, sets a 3-inch maximum cable spacing and posts no more than 4 feet on center, tighter than the 6 to 8 feet used for standard wood or aluminum railings.
A cable manufacturer’s wood-frame requirements sheet goes further, recommending cables no more than 3 inches apart and posts or vertical members no more than 3 feet apart to limit deflection. It also notes that each cable carries a tension load above 300 pounds, so the frame has to be built strong enough to hold it. Grand Rapids, Minnesota, puts numbers on this: a rail with nine cables at 300 pounds each pulls roughly 2,700 pounds on the end posts.
That is why cable runs need beefy, well-anchored end posts. Intermediate posts can be lighter, but the corners and ends do the heavy lifting. If you are weighing the look against the extra posts, our cable deck railing buying guide walks through it.
How to measure post spacing correctly
Most spacing mistakes are measuring mistakes. Posts are specified on center, which means from the middle of one post to the middle of the next. DecksDirect points out the consequence: if you measure 6 feet of clear distance from the near side of one post to the near side of the next, a 6-foot on-center rail kit will not reach.
Here is a simple process:
- Mark the corner posts first. Corners are usually the largest posts and anchor the layout.
- Measure each run corner to corner, center to center. Write down every run separately.
- Divide each run into equal bays. Divide by your maximum, round up to the next whole number, then divide again. A 17-foot run with a 6-foot limit needs 3 bays of about 5 feet 8 inches, which means two line posts between corners.
- Keep stair posts in mind. Stairs have their own guard and handrail rules, covered in our deck stairs code guide.
- Adjust for gates and openings. A stair landing or gate opening usually needs a post on each side, so lay those out before you divide the remaining span.
Equal bays also look better. A single odd short bay at the end of a run is the first thing a visitor notices.
Post types you will place
Railings use three kinds of posts, per Lowe’s buying guide: corner posts at the deck’s corners, typically larger for extra support, end posts where a railing section terminates, and line posts spaced along the run. Spacing limits apply between all of them, so a corner post counts as one end of a bay.
Spacing and openings work together
Post spacing is only one dimension of a safe guard. The 4-inch sphere rule applies to every gap, including those between balusters and posts, so the baluster layout depends on your post layout. Stair guards have a slightly different allowance, which we explain in our guardrail vs. handrail guide. Height is the other half, covered in our deck railing height guide.
A quick baluster check: choose your bay length, subtract the width of the posts, then divide the clear gap by the baluster width plus a gap under 4 inches. Aim for equal gaps rather than cramming a final gap right at the limit. Pickets for horizontal rails and cable need special care, as we explain in our horizontal railing safety article.
Post connections matter as much as spacing
A 6-foot span with a weak connection is worse than a 5-foot span with a solid one. Both Chesapeake and Livonia call for hold-down anchors rated at 1,800 pounds, installed per manufacturer instructions. Livonia prohibits notching guard posts, and Grand Rapids says studies have shown notched posts fail to meet the 200-pound horizontal load its code requires.
Inspection specialist Daniel Friedman, writing on Inspectapedia, explains that posts continuous from footing to rail are the strongest but often impractical. More commonly, posts bolt through the rim joist or beam, and the rim joist needs reinforcement so it cannot rotate when force hits the railing. Through-bolts are preferred over lag screws alone.
The same principle of solid fastening applies to the handrails you grip on stairs. If you are anchoring a rail into a wall or solid backing, handrail wall anchor options show how much fastener choice matters.
This is also why a railing replacement should start with the posts. If your existing posts are loose, notched or rotted at the base, new spacing will not fix them. We go into this in our guide to inspecting posts when you replace deck railings.
What Everett, Washington expects
If your deck is in Everett, the City’s permit services residential decks page states that plans must show the guardrails, including guard height, post spacing and picket spacing. It also says a licensed architect or engineer is required when the deck has more than one level, supports a hot tub, has a walking surface more than 14 feet above ground, or falls outside the prescriptive method in Section R507 of the 2021 IRC.
In plain terms: put your post spacing on the drawing, make it a number you can defend, and confirm any unusual design with the city before you build. Setbacks can also change where your railing ends up, which we cover in our Everett deck setbacks article. Rules are updated from time to time, so check with the City of Everett for the current requirements on your project.
Our Northwest climate adds another consideration: wet winters and wind exposure. If your deck sits on an open lot or a slope, see our notes on wind resistant deck railing.
Common spacing mistakes
- Stretching to the maximum everywhere. Use equal bays under the limit.
- Measuring edge to edge. Remember on-center.
- Mixing parts from different systems. Each system has its own tested spans.
- Notching 4x4 posts over the rim. Notched posts are widely flagged as a weak point.
- Skipping the end posts’ strength on cable rails. Cable tension loads end posts hard.
- Planning posts after the decking is laid. Post locations should be settled with the framing so blocking and connections are in the right places.
Perspective
We think about railing posts before anything else, because everything the homeowner sees and touches hangs on them. A common pattern we see in deck replacements is a handsome new surface with the old railing posts left in place, and those posts are often loose or poorly attached.
Our in-house crew, not subcontractors, lays out posts as part of the framing plan. That way spacing, blocking and connections are decided together, and the permit drawing matches what gets built. We would rather add one extra post than push a span to its limit, because a railing that feels solid is a railing families actually trust when they are entertaining.
For the Northwest, we favor materials and hardware chosen for wet weather, and we design our installations to be backed by our warranty. If you are unsure which spacing fits your design, a quick look at the site plan usually answers it.
Vlad
Want a railing laid out right the first time?
We design and build deck railing systems in Everett and surrounding communities, from the permit drawing through installation. Our deck railing systems service covers post layout, materials such as composite, PVC and cedar, stairs and lighting. If you are replacing the whole deck, see our deck replacement page.
To talk through your project, start at Cactus Decking and request a consultation.
FAQ
What is the maximum spacing for deck railing posts?
For 4x4 wood posts, 6 feet on center is the figure shown in official deck guides such as Chesapeake’s. Some local guides allow up to 8 feet on center, as in Transylvania County’s. Your local building department sets the number that applies to you.
How far apart should posts be for cable railing?
Plan on 4 feet on center or less. Grafton, Massachusetts, specifies posts at 4 feet maximum with cables no more than 3 inches apart. Some cable manufacturers recommend even closer posts, so follow your system’s instructions.
Does the building code require a specific railing post spacing?
Not as one universal number. Codes set guard height, opening limits and a load the guard must resist, and local deck guides translate that into prescriptive details such as 6 feet for 4x4 posts. In Everett, plans must show your post spacing, so confirm it with the city.
Is deck post spacing measured from the center of the posts?
Yes. Spacing is on center, from the middle of one post to the middle of the next. Measuring the gap between posts gives you a shorter number than the rail kit or panel will need.
Can I use 4x4 posts if they are notched over the rim joist?
It is better not to. Livonia’s guide prohibits notching guard posts, and Grand Rapids says notched posts have failed the 200-pound load test. Bolt posts through the framing and reinforce the rim joist instead.
Sources
- Transylvania County Deck Guide
- City of Grand Rapids, MN: Constructing Safe Guardrails
- City of Everett Residential Decks
- Aluminum railing installation instructions
- Cable railing wood frame requirements
- Deck railing calculator reference
- Deck railing post spacing guide
- Deck railing posts guide
- Deck railing post connections
