A post level is a small, two- or three-sided spirit level that straps or clamps to a post, pipe, or stud so you can check plumb and level on adjacent faces at the same time, hands-free; it typically has vertical, horizontal, and sometimes 45-degree vials, fold-out arms, and magnets or elastic bands to help install straight, upright structures quickly and accurately.
What Is a Post Level?
A post level is a compact leveling tool designed to sit on the corner of a post, pipe, or stud and show you if it is perfectly upright (plumb) and horizontal (level) at once. It uses bubble vials—clear tubes filled with liquid and an air bubble—to indicate alignment. Because it clamps, straps, or magnetizes to the workpiece, it frees your hands to adjust and brace the post without juggling a separate level.
In simple terms: plumb means straight up and down, and level means flat across. A post level helps you get both right with less fuss.
How It Works
Most post levels have two or three vials set at 90 degrees. When the bubble sits between the marked lines, that face is aligned. By checking adjacent faces simultaneously, you avoid tilting a post one way while unknowingly throwing it off in the other direction. Many models include:
- Fold-out arms that meet at a right angle and hug corners
- An elastic strap or hook-and-loop band to hold the tool in place
- Magnets for attaching to metal posts or pipe
- High-visibility housing and vial markings for easy reading in daylight
Some versions add a third vial set at 45 degrees for tasks like railings or braces.
Common Uses in DIY and Home Projects
You’ll reach for a post level any time you need straight, upright supports:
- Setting fence and gate posts in concrete or tamped gravel
- Plumbing deck and porch support posts
- Installing mailbox posts and lamp posts
- Aligning pergola and arbor columns
- Standing up basketball hoop poles and clothesline posts
- Checking studs and corner framing during wall layout
- Plumbing conduit or round pipe for handrails
Because it stays attached while you adjust, it’s especially helpful if you’re working solo.
Types and Variations
Post levels fall into a few broad categories:
- Two-sided (L-shaped) plastic: Folds around a corner; compact and affordable. Good for 4x4 and 6x6 posts.
- Three-sided (wraparound): Covers three faces at once; very stable on square posts.
- Magnetic models: Embedded magnets grip steel posts, pipe, and metal studs.
- Strap-on models: Elastic or hook-and-loop band secures to wood, vinyl, or composite posts.
- With 45-degree vial: Adds an angled reference for braces and railings.
- Heavy-duty/contractor grade: Thicker ABS or aluminum body, replaceable straps, higher accuracy vials.
Accuracy is often expressed as 0.5 mm/m (roughly 0.0005 in/in). For typical fence and deck work, this is more than adequate.
How to Choose a Post Level
Consider these points before you buy:
- Post material: Choose magnets for metal posts; choose a strap for wood, vinyl, and composites.
- Size and fit: Ensure the arms or faces contact squarely on 4x4 or 6x6 posts you plan to set.
- Vial visibility: Look for bright markings and UV-resistant vials that are easy to read in sunlight.
- Strap quality: A wide, adjustable strap holds better and lasts longer than a thin rubber band.
- Durability: Impact-resistant housing and protected vials survive jobsite drops.
- Accuracy rating: Aim for 0.5 mm/m or better for structural posts.
- Storage: Folding arms and a compact profile fit in a tool bag without snagging.
Price-wise, expect budget models in the $5–$10 range and more rugged options around $15–$30.
How to Use a Post Level (Step-by-Step)
- Prepare the hole: Dig to the recommended depth and widen the base if using concrete. Add a few inches of compacted gravel for drainage.
- Rough set the post: Place the post, add a little backfill or braces so it stands with minimal wobble.
- Attach the level: Wrap the strap or let the magnets grip. Position the tool so both vertical vials are visible.
- Adjust to plumb: Nudge the post until both vertical bubbles are centered at the same time. If one centers and the other doesn’t, you’re leaning in one direction.
- Check twist: On square posts, confirm the faces are oriented correctly relative to string lines or neighboring posts.
- Secure the post: Add temporary braces or clamps to keep it plumb.
- Backfill or pour concrete: Fill in lifts, checking the vials after each step. Re-center the bubbles if the post shifts.
- Final check: Before the concrete sets, confirm plumb in both directions again. Leave the level on for a few minutes to monitor any movement, then remove and clean it.
Maintenance and Care
- Keep it clean: Rinse off mud and grit so the tool seats flat against surfaces.
- Protect the vials: Store in a pouch or tool bag pocket to avoid scratching or cracking.
- Replace worn straps: Elastic loses tension over time; swap it to keep a snug fit.
- Quick accuracy check: Place on a plumb edge, note the bubble, rotate the level 180 degrees on the same edge. If the bubble reads differently, the tool is out of calibration.
- Avoid prolonged heat: Don’t leave it on a hot dashboard; extreme heat can affect plastics and seals.
Common Mistakes to Avoid
- Checking only one face: Always confirm both vertical vials are centered together.
- Reading at an angle: Look straight at the vial to avoid parallax (a skewed reading from viewing off to the side).
- Level on edges, not faces: Chamfered or rounded post edges can skew contact. Place the tool on flat faces or use the strap for consistent seating.
- Ignoring twist: A post can be plumb but rotated. Align faces with string lines, fences, or beam brackets.
- Letting the hole backfill move the post: Re-check after tamping soil or adding concrete; brace right away if it shifts.
- Trusting bowed lumber: Sight down the post; severe bows or twists make it hard to achieve a straight result even if it’s technically plumb.
Related Tools and Concepts
- Torpedo level: A small, straight level for shelves and short runs; great for tight spaces but doesn’t read two directions at once.
- Box level (or I-beam level): Longer level for walls, floors, and beams.
- Line level: Clips to a string line to check level over distance.
- Plumb bob: Weighted string that indicates vertical alignment without bubbles or electronics.
- Laser level (cross-line or rotary): Projects level/plumb lines across the job; ideal for layout and aligning multiple posts.
Real-World Examples
- Privacy fence: Set the first corner post with a post level, brace it, and let the concrete set. Use a string line between corners and the same level to plumb intermediate posts quickly.
- Deck build: Plumb 6x6 support posts in brackets before attaching beams. Keep the level on while you tighten hardware to catch any movement.
- Mailbox upgrade: With mixed gravel and a concrete collar, use the post level to maintain plumb as you tamp and finish the set to the correct height.
- Pergola columns: Strap the level to each column and adjust both vertical vials while aligning the column faces with the beam layout for a clean, square look.
- Metal handrail post: A magnetic post level holds to the round pipe so you can keep both hands on the wrench while you plumb and tighten anchors.
A post level speeds up any job that needs straight, upright supports and helps you get repeatable, professional-looking results even if you’re working alone.