String Trimmer Line Sizes | Match The Diameter To The Job

Choosing string trimmer line sizes comes down to matching the diameter to two things: what your trimmer head accepts and what you’re cutting. Thin line handles light grass and edging, while thick line powers through brush. The trimmer’s own limits matter more than the job, though—use a line that’s too thick for the head and you’ll strain the motor or cause constant jams.

Common Line Diameters And What Each One Cuts

Line diameter is measured in inches, and most residential trimmers use one of three sizes: 0.065, 0.080, or 0.095. Heavier commercial units step up to 0.105, 0.130, or 0.155.

STIHL’s own guide lists standard diameters of.065,.080,.095,.105,.118,.120,.130, and.155 inches. The practical breakdown by job:

• Light grass and edging: 0.065–0.080 in
• General residential trimming: 0.080–0.110 in
• Heavy weeds and thick stems: 0.095–0.110 in
• Brush and dense vegetation: 0.130 in or larger

Thicker line generally calls for a more powerful trimmer. Small electric and battery units pair naturally with thinner line, while gas and higher-voltage machines can feed the heavy stuff.

Does Line Size Matter That Much?

Size matters, but it’s not the whole story. Line shape, head design, and raw power output all affect how a trimmer performs. A thicker line on an underpowered motor will bog down and cut worse than a correctly sized thin line spun at full speed.

The most common mistake is buying the wrong diameter because labels mix units. The same size may be printed as 0.080 inches on one package and 2.0 mm on another—they’re identical, but shoppers sometimes grab the wrong one when the units don’t register.

Never rely on a guess. The trimmer head physically limits what fits, and the manufacturer’s spec is the final word.

How To Find Your Trimmer’s Recommended Line Size

The fastest way to the right diameter is the owner’s manual. If you don’t have it, check the trimmer head or spool—most manufacturers print the recommended size right on the label.

Substitute a larger diameter only if the head supports it. Oversized line can reduce cutting performance, strain the machine, or prevent the line from feeding out of the head at all. When in doubt, stick with the size that came pre-loaded on the spool.

For anyone maintaining a commercial unit or tackling serious acreage, we’ve tested the top options in our roundup of the best commercial string trimmer line for heavy-duty work.

Matching Line To Your Trimmer Type

Battery and corded electric trimmers usually run 0.065–0.080 inch line. Mid-range gas trimmers handle 0.080–0.095. Professional gas and high-voltage battery units take 0.105 and up. Check your model’s specs before buying, and if you’re between two sizes, the thinner one is the safer pick for machine longevity.

String Trimmer Safety Basics

Trimmer line throws debris at high speed, and eye protection is non-negotiable. Public safety materials recommend eye protection meeting or exceeding ANSI Z87.1. North Carolina’s DOT guidance for string trimmer and brush cutter operation goes further: safety glasses plus a face shield or screen. Wear both when cutting anything heavier than grass.