How to Install Railing Posts on a Deck in 4 Steps

Don’t skip these safety steps

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Catherine Hiles
Written by Catherine Hiles
Contributing Writer
Updated May 29, 2025

This project is costly to DIY, and making a mistake could immediately double the cost. Call a pro for a job done well the first time.

SKILL LEVEL
Simple
COMPLETION TIME
1 day
COST
$70–$245
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What you'll need:
TOOLS
  • Tape measure
  • Pencil or chalk
  • Circular saw
  • Drill
  • Clamps
SUPPLIES
  • 4x4 deck posts
  • Carriage bolts
  • Washers
  • Nuts

Deck railings are important safety features—and if your deck is over 30 inches off the ground, building codes require a deck railing height of at least 36 inches. If you’re building a deck as a DIY project, it’s essential to know how to install railing posts on a deck to ensure the railing is sturdy and up to code. This guide outlines the precise steps for correctly installing railing posts.

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  1. Calculate the Correct Post Height

    13 parts of a deck illustrated, including beams, posts, and decking

    If you want 36-inch railings and have a 10-inch joist, your deck post must be 46 inches tall. Allow for any additional height as well; for example, you might want the deck posts to rise a couple of inches above the deck railing, increasing the post height to 48 inches.

  2. Cut the Posts to Size

    Man measuring boards planks
    Photo: knape / E+/ Getty Images

    Use your tape measure and mark the posts at the cutting point with a pencil or chalk. Then, cut the posts to the correct length using a circular saw. You can cut them straight across or at a slight angle if you prefer the look.

  3. Mark and Drill the Holes

    You must drill holes in the posts to attach them to the deck joists. 

    Mark one hole about an inch and a half from the top of the deck joist and another an inch and a half from the bottom. Stagger the holes to prevent the posts from splitting.

    Once you have marked the holes in the proper locations, drill them. Use a drill bit that’s the same diameter as the carriage bolts you’ll use to attach the posts to the deck joists.

  4. Secure the Posts to the Deck

    Wooden deck patio surface
    Photo: JamesBrey / E+ / Getty Images

    Once you’ve drilled the holes and cut the notches, you’re ready to secure the posts to the deck. 

    First, clamp the posts in place and use a post level to ensure they are straight. Then, drill through the existing holes into the joists and hammer the carriage bolts into place. Finally, secure the carriage bolts with a washer and nut on the inside of the deck joist.

When to Install Railing Posts on a Deck

The best time to install railing posts on a deck is during the structure’s initial construction. It’s much easier to install the railing posts before the decking, when the deck is still just a frame. Installing railing posts on an existing deck may require removing the decking to ensure a proper fit.

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DIY vs. Hiring a Pro

An experienced DIYer can install rail posts on an existing deck by following the steps above and using the proper tools. However, novice DIYers might find this project intimidating, or they may simply not have the time to tackle it themselves, even if they are familiar with how to build a deck railing.

If you’re not confident in your DIY skills, a pro can install railing posts quickly and easily. By hiring a local deck builder, you can be sure that the railing posts are secure, ensuring your deck railings are safe and sturdy. Plus, since a pro has experience installing hundreds of decks, the finished project may be more aesthetically pleasing than a DIY job. The labor cost to install a new deck railing runs between $10 and $50 per linear foot.

Frequently Asked Questions

While building your deck, you might come across something called the four-inch sphere rule. Essentially, this railing requirement for a deck states that a four-inch ball should not be able to fit through any gap in the deck railings. The gap between spindles and between the decking and the bottom of the railing must be less than four inches to prevent small children or pets from squeezing through the gap.

Space deck handrail posts four to six feet apart. If the posts are more than six feet apart, the railing will be less able to withstand lateral forces and is more susceptible to breaking. Additionally, railing posts that are more than six feet apart may not be up to code, and you may face fines and be required to reinstall the posts to bring them up to code.

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Learn more about our contributor
Catherine Hiles
Written by Catherine Hiles
Contributing Writer
Catherine is a content writer specializing in home improvement, home finance, and personal finance. She is passionate about making complex topics more digestible for the average reader. Catherine’s work can be found on BobVila.com and TIME Stamped, among others.

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