How to Set and Cut Posts for Decks to Build a Sturdy Frame

To build your own deck, start by setting and cutting the posts that will be the frame for your new favorite hangout. Our step-by-step instructions will show you how to set deck posts that are plumb and square, plus how to cut deck posts to a level height.

back of taupe house with upper deck and lower patio sitting area
Photo: Peter Krumhardt
Project Overview
  • Working Time: 10 hours
  • Total Time: 3 days
  • Skill Level: Intermediate

Setting the posts for your deck requires careful work, but it can also be exciting because the posts are the first visible sign that your new deck is going up. Although you still have a lot of work to do after you set deck posts, getting them up can make you feel like you're halfway there.

Deck posts must be plumb, so they have to start out with square ends. Check the bottom of each post with a speed square and cut it if necessary. Dip cut ends in a preservative before setting them in the anchors and let the preservative soak in overnight.

To make the job go quickly, do everything in stages—square all the deck posts, set them in the anchors with a temporary brace. Next, plumb, align, and brace all of them, letting their height run wild before marking and cutting them to a consistent height.

Setting deck posts will go more than twice as fast if you have someone help you. Two helpers are even better; you won't have to move back and forth from one post to another to adjust them. Follow along with our steps for setting and cutting deck posts to get started on your backyard makeover.

What You'll Need

Equipment / Tools

  • 1 Speed square
  • 1 Carpenter's pencil
  • 1 Miter saw or circular saw
  • 1 Framing hammer
  • 1 Post level
  • 1 Mason's line
  • 1 Clamps
  • 1 Wrench
  • 1 Drill
  • 1 Water level
  • 1 Measuring tape
  • 1 Reciprocating saw

Materials

  • 1 Lumber
  • 1 Wood preservative
  • 1 Deck post anchor
  • 1 Nails
  • 1 1x4 boards
  • 1 Fasteners
  • 1 Masking tape

Instructions

  1. Square and Preserve Ends of Deck Posts

    marking wood with pencil and yellow speed square
    Larry Johnston

    The day before you set the posts, make sure their ends are square. Mark the cut lines with a speed square and make the cuts with a miter saw or circular saw. Dip the cut ends in wood preservative and let them sit overnight.

  2. Set Deck Posts

    two people setting a post
    Larry Johnston

    Set each deck post in its anchor. While someone holds it plumb, drive one nail through the anchor hole and about halfway into the post. This will keep the bottom in place but allow you to move it when you plumb it. Tack 1x4 bracing to the post and stake in position.

  3. Brace and Plumb Deck Posts

    man clamping brace on post
    Larry Johnston

    When you've set and temporarily braced all the deck posts, restring the mason's lines on the marks that represent the outside edge of the posts. Clamp a second 1x4 brace to the post and stake it. Plumb each deck post with a post level, keeping its outside face against the mason's line.

  4. Align Deck Posts

    crouched man sighting down the mason's line
    Larry Johnston

    Recheck the post alignment by sighting down the mason's line. Replumb any post that looks out of line and adjust the bottom of the post if necessary. If you have a post that's plumb but slightly bowed (no more than 1/8 inch), you can force it into place when you install the beams or joists.

    Project tip: Adjustable post anchors are made to be moved—right up to the last minute. To make an adjustment insert an open-end wrench in the slot and loosen the nut just slightly. Tap the post into place with a hammer and a piece of 2x4 scrap, and retighten the nut.

  5. Anchor Deck Posts

    hammer driving fastener into post anchor
    Larry Johnston

    Drive the remaining fasteners into the post anchor. Some anchors are made to accept nails or screws only. Others are fabricated to accept a lag screw also. Predrill for the lag screw before driving it.

  6. Mark Level Line

    person marking post
    Larry Johnston

    Use a water level to establish the height of each post. Fasten one end of the water level so the water line is even with the bottom of the ledger (or level with whatever edge your plan prescribes). Hold the water level on each post and mark the post at the water line. Transfer the mark around the posts.

  7. Make Cut Line

    using pencil and tape measure to mark cut line on post
    Larry Johnston

    You can mark the cut line for the posts by using the depth of the joist and/or beam, depending on your construction plan. Starting at the line that is level with the bottom of the ledger, measure down the depth of the joist and mark this point.

  8. Mark All Deck Posts

    marking cut line on post with speed square
    Larry Johnston

    Transfer the cut line to all the faces of the deck posts, using a speed square and a carpenter's pencil. Make this line dark enough so you can see it when the sawdust flies. You will need to be able to see the line to keep the blade from wandering.

  9. Cut Deck Posts

    man cutting post with reciprocating saw
    Larry Johnston

    Holding the weight of a circular saw at right angles to the post can prove cumbersome (and even dangerous), especially when standing on a ladder for a raised deck. A reciprocating saw will prove more accurate. Keep the shoe of the saw on the surface of the post and make sure the blade cuts straight along the line.

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