How to Use a Level

Written & researched by Derek Holt Home & Appliances Editor

Updated February 2026

To use a level, place it flat against the surface you are checking and read the bubble in the vial: the surface is level or plumb when the bubble sits exactly centered between the two lines printed on the vial. A level tells you whether something is perfectly horizontal (level) or perfectly vertical (plumb) using a sealed vial of liquid with a trapped air bubble. If the bubble drifts to one side, that side is high — adjust until the bubble centers. That single reading is the whole skill, and the rest is knowing which vial to read and how to trust your tool.

We do not test or physically handle the products we cover; our guidance draws on manufacturer guidance and the aggregated experience in thousands of owner reviews, as explained in how we rank.

The parts of a level

A basic spirit level is a straight bar, usually aluminum, with one or more vials set into it. Each vial is a small sealed tube of colored liquid with an air bubble inside, and each has two reference lines printed around it. Understanding the layout makes reading it obvious:

• The center vial reads level (horizontal). It is oriented lengthwise so it responds when the bar lies flat.
• The end vial(s) read plumb (vertical). They are oriented crosswise so they respond when the bar stands upright.
• A 45-degree vial, on many levels, reads a 45-degree angle for diagonal work.

The liquid is slightly curved so the bubble always floats to the highest point. When the surface is true, the highest point is the middle, and the bubble rests between the lines.

Reading the bubble correctly

Reading a level is simple, but two small errors cause most bad readings. Here is the reliable method:

1. Set the level on the surface so it sits flat with no rocking. Wipe away grit first — a crumb under one end throws the whole reading off.
2. Look at the vial straight on, at eye level. Viewing from an angle makes the bubble look off-center when it is not. This parallax error is the number-one reading mistake.
3. Find the bubble. Centered exactly between the two lines means the surface is true.
4. Read which way it drifts. The bubble moves toward the high end. If it sits to the right, the right side is high — lower it, or raise the left, until the bubble centers.

That is the entire reading. Whether you are checking level or plumb, "centered between the lines" is always the target; only the orientation of the tool changes.

Level vs plumb: two things, one tool

These two words trip people up, so it is worth fixing them clearly. Level is perfectly horizontal — side to side — like a shelf, a countertop, or a washing machine. You check level by laying the tool flat and reading the center vial. Plumb is perfectly vertical — straight up and down — like a door frame, a fence post, or the side of a picture frame. You check plumb by holding the tool upright against the vertical surface and reading the end vial.

The same physical bubble-centered rule applies to both. A door frame that is plumb and a shelf that is level are both just "bubble between the lines," read on the appropriate vial. Keeping the two words straight is mostly what separates confident level use from guesswork.

Types of level and when to use each

Different jobs call for different levels. Here is how the common types compare so you reach for the right one.

Spirit levels (torpedo, box, and long) are the everyday workhorses — no batteries, instantly readable, and accurate. A torpedo level is the small one for tight spaces and is often magnetic so it clings to pipes and metal. A laser level earns its place when you need a straight reference across a whole room or between points too far apart to bridge with a straightedge. For a single shelf, a spirit level is faster and simpler; for a run of cabinets or a wall of frames, the laser keeps everything aligned to one line. The Power Tools & Workshop hub compares levels by how owners rate them.

Why length matters

A longer level gives a more accurate reading over a longer span, and this is the mistake beginners make most. A short level can read perfectly level while sitting on a small high spot, even though the whole surface slopes away on both sides. The tool only knows about the span it touches. As a rule, use a level at least as long as, or longer than, the object you are checking. To level a four-foot shelf, use a level close to four feet, or bridge a longer straightedge across a shorter level. For an appliance foot, a torpedo level is fine because the foot itself is small.

Check your level for accuracy first

A level you cannot trust is worse than no level, because it makes you confident while you install things crooked. Levels drift out of true if dropped or knocked around, so verify yours with the flip test before important work — it takes ten seconds.

1. Set the level on a flat surface and note exactly where the bubble sits relative to the lines.
2. Rotate it 180 degrees end-to-end in the same spot, so left becomes right.
3. Read the bubble again. If it sits in the same place, the level is accurate. If it now reads differently, the tool is off.
4. Repeat for plumb by flipping the level against a vertical surface and comparing.

Some levels have adjustable vials you can recalibrate; most inexpensive ones do not, so a failed flip test means replace it. Either way, do this check periodically and after any drop.

Common tasks step by step

Here is how the reading translates into real jobs.

Hanging a shelf level:

1. Hold the shelf or a bracket at the height you want and rest the level on top.
2. Tilt the shelf until the center bubble sits between the lines.
3. Mark the screw or bracket positions with a pencil while it reads level.
4. Recheck with the level after fastening, since drilling can shift things slightly.

Leveling an appliance (washer, refrigerator, range):

1. Set a torpedo or short level on top of the appliance, first front-to-back, then side-to-side.
2. Read which corner is low.
3. Turn the adjustable feet up or down until both directions read level.
4. A level appliance runs quieter, drains properly, and vibrates less, so it is worth the minute.

Hanging a picture straight: rest the level along the top of the frame after it is on the wall, nudge one side up or down until the bubble centers, then mark or adjust the hook. For a row of frames, a laser level projects one line to hang them all to.

Practical tips for accurate readings

• Clean the surface and the level. Grit under either end tilts the reading.
• Always read at eye level, straight on. Parallax is the silent cause of "level" work that turns out crooked.
• Use both hands to hold long levels flat so the middle does not sag or the tool does not rock.
• Mark while it is true. Hold the level in position and mark your reference before you move it.
• Recheck after fastening. Screws and nails can pull a piece slightly out of true as they tighten.

It is also worth understanding what the two vial lines actually tell you beyond simple pass-or-fail. The distance the bubble sits from center is roughly proportional to how far out of true the surface is, so a bubble just kissing one line is only slightly off, while a bubble jammed hard against the end is badly out. On careful work — a countertop, a run of cabinets, a door — you want the bubble dead center, not merely touching a line. On rougher work like garden edging or a temporary bracket, a bubble sitting between the lines but not perfectly centered is usually good enough. Learning to read that degree of tilt, rather than treating the level as a yes-or-no device, is what turns a beginner into someone who can judge how much correction a surface really needs.

Bringing it together

Using a level comes down to a single habit: rest the tool on the surface, read the correct vial straight on, and adjust until the bubble sits centered between the lines. Know that level means horizontal and plumb means vertical, pick a tool long enough for the job, and run the flip test so you can trust what the bubble tells you.

Related: the Power Tools & Workshop hub compares levels by owner ratings, and how we rank explains our research-only method. Browse more guides on the resources index.