String Trimmer Line Sizes and Types

Trimmer line is sold by diameter, from .065 inch for light work to .155 inch for heavy work; use a size your trimmer head lists, then pick a shape.

By Damien VolkmanContributing writer.

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Bar chart of trimmer line diameters in millimeters, from .065 inch at about 1.7 mm to .155 inch at about 3.9 mm. — Round trimmer line diameters Stihl lists, converted to millimeters. Chart by Wiki Shopping.

The short answer

String trimmer line is sold by its diameter in thousandths of an inch: .065, .080, .095 and so on. Your trimmer head only accepts certain sizes, so check the head or the manual first. Then choose the shape: round for everyday edging, edged shapes for tougher weeds and brush.

Trimmer line sizes

Stihl sells its round line in seven diameters. Here they are with the metric size (1 inch is 25.4 mm; Stihl itself lists .095 inch as 2.4 mm):

Diameter	Metric
.065 in	about 1.7 mm
.080 in	about 2.0 mm
.095 in	2.4 mm
.105 in	about 2.7 mm
.118 in	about 3.0 mm
.130 in	about 3.3 mm
.155 in	about 3.9 mm

On the Stihl trimmer heads below, the listed sizes run from .065 to .120 inch. Other line makers sell similar diameters, but always buy the size your head lists rather than the size of the line you used last time.

Match the line to your trimmer head

The size that fits is set by the cutting head, not by the brand of line. Stihl's product pages show how this works:

FS 38 gas trimmer: the AutoCut 5-2 head takes .080 inch line as standard, while the AutoCut C 6-2 head takes .095 inch, with .080 as an option.
FS 56 gas trimmer: depending on the head, standard line runs from .095 to .120 inch, with .080 to .105 as options on some heads.
FSA 50 battery trimmer: .080 inch standard line on its AutoCut C 3-2 head.

If you are unsure, stay with the standard size printed for your head. Stihl's own line is made to fit Stihl and other brands' heads, but the diameter still has to be one your head lists.

Trimmer line shapes

Diameter is half the story. The cross section changes how the line cuts:

Shape	What Stihl says it does	Good for
Round	Standard, multi-purpose profile that resists fraying and welding	Lawn edges and general mowing
Square	Sharp edges for a cleaner, almost knife-like cut	Thick, woody grass and tough weeds
Pentagon (five sided)	Hard edges plus the wear resistance and easy respooling of round line	Matted weeds and thick brush
Grooved "quiet" line	Spiral grooves cut wind noise	Battery and corded trimmers, noise-sensitive areas
Cruciform (cross shaped)	Three-component polyamide built for tough jobs	Heavy professional use

Battery trimmers and line

The battery FSA 50 above uses .080 inch line, so check a battery trimmer's head before buying a spool sized for a gas model. Stihl also points its grooved quiet line at battery and corded-electric trimmers, since those tools run much quieter than gas models, and at properties with noise restrictions.

How we count

Wiki Shopping lists 67 string trimmers under patio, lawn and garden as of October 27, 2026, from our read-only listing data. Of those, 16 state 20V and 12 state 21V; 14 list a 2Ah battery and 7 a 4Ah battery. Listings that do not state a value are left out of those counts, and the counts change as listings are added or removed.

String Trimmer Line Sizes and Types

The short answer

Trimmer line sizes

Match the line to your trimmer head

Trimmer line shapes

Battery trimmers and line

How we count

Shop by spec

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