What Size Trimmer Line Do I Need?

Use the line diameter your trimmer’s manual or head lists, and pick within that range by job. As a quick rule: 0.065 inch for light cordless and corded trimmers, 0.080 inch for most mid-size gas and 40-volt and above battery trimmers, and 0.095 inch or thicker for powerful gas and pro-grade trimmers clearing heavy weeds and brush. Going thicker than your trimmer is built for slows the head, drains batteries, overheats motors and can jam the spool. Going thinner than it needs breaks constantly. This guide explains how to find your size, how diameter and shape change cutting, and a sizing chart by trimmer type.

In this guide

1. How to Find the Right Size for Your Trimmer
2. Trimmer Line Sizing Chart
3. What Each Diameter Does Well
4. Line Shape: Round, Twisted, Square and Star
5. Choosing by Job
6. Materials and Quality
7. Fit Problems and How to Fix Them
8. How Much Line to Wind
9. Head Type Changes the Answer
10. Edging vs Trimming
11. Safety Notes
12. Buying Tips
13. Frequently Asked Questions

How to Find the Right Size for Your Trimmer

1. Check the head or spool. Many trimmer heads have the acceptable diameter range molded into the plastic, for example “0.080–0.095 in.”
2. Check the manual. The specifications section usually lists the recommended line diameter and sometimes a maximum.
3. Check the replacement spool part number. Pre-wound spools list their diameter on the package.
4. Measure the old line. A caliper gives the exact diameter. Without one, compare to a known sample at the hardware store.
5. Look at the eyelets. The line should pass through easily but not loosely. If you have to force it, it is too thick.

If none of those work, look up the model number on the manufacturer’s site. Do not guess thicker; the safest test is to try the smallest size in the common range for your trimmer type and step up only if it breaks too often.

Trimmer Line Sizing Chart

Trimmer type	Typical line diameter	Best for
Light cordless (12 to 20 volt)	0.065 inch, sometimes 0.050 to 0.065	Edging and light trimming on small lawns
Corded electric	0.065 inch, some 0.080	Grass trimming close to the house
Mid-range cordless (36 to 60 volt)	0.080 inch, some 0.095	Average suburban yard, light weeds
Small gas (under about 25cc)	0.065 to 0.080 inch	Grass and light weeds
Mid-size gas (about 25 to 30cc)	0.080 to 0.095 inch	Mixed grass and thicker weeds
Pro-grade gas and high-power battery	0.095 to 0.105 inch	Dense weeds, fence lines, ditches
Brushcutter heads	0.105 to 0.155 inch	Heavy brush, field clearing

These are typical ranges, not rules for every model. Always defer to what your trimmer specifies. If you are choosing a trimmer and want to understand how the categories differ, see our guide to types of string trimmers.

What Each Diameter Does Well

0.065 inch: light duty

The standard for small electric and battery trimmers. It spins fast with little motor load, so batteries last longer and the cut is clean on turfgrass. It breaks easily against concrete, fences and tough weeds. Ideal for small, well-kept lawns where you mostly trim edges and around beds.

0.080 inch: the all-rounder

The most common size for homeowner gas trimmers and mid to high-voltage cordless models. It handles grass and moderate weeds and lasts noticeably longer than 0.065 against hardscape. If your trimmer accepts a range that includes 0.080, it is a good default.

0.095 inch: heavy residential

Built for overgrown areas, tall weeds, thick-stemmed growth along fences and larger properties. It needs a strong gas engine or a high-power battery trimmer to keep head speed up. On a weaker trimmer, it bogs down, leaves ragged cuts and can overheat the motor.

0.105 inch and up: commercial and brush

Used by landscape crews and on brushcutters clearing ditches, roadsides and fields. Most homeowner trimmers cannot spin this line fast enough to cut well, and many heads will not accept it. If you regularly need this weight, consider a metal blade attachment on a compatible trimmer.

Line Shape: Round, Twisted, Square and Star

Shape	How it cuts	Best use	Trade-off
Round	Tears and slaps grass	General trimming, hardscape edges	Less clean cut; louder at high speed
Twisted	Quieter, slightly sharper cut	Residential grass and light weeds	Costs a little more than round
Square	Sharp edges slice stems	Thick weeds, overgrowth	Wears faster against concrete
Star or multi-sided	Several cutting edges	Dense grass and weeds	Edges dull with hardscape contact
Serrated	Saw-like edge	Heavy weeds and brush	Breaks more easily on fixed heads

Shape matters most when you are pushing the limits of your trimmer. A shaped line at the same diameter cuts more efficiently than round, which can let a lighter trimmer handle tougher growth without stepping up in thickness. For trimming next to driveways, curbs and walls, round or twisted line lasts longest.

Choosing by Job

• Small lawn, edging only: 0.065 inch round or twisted.
• Typical suburban yard with beds, fence and driveway: 0.080 inch twisted or round.
• Lots of trimming along hardscape: round line in the thickest size your trimmer handles comfortably.
• Overgrown weeds, rural fence lines: 0.095 inch square or star, on a capable trimmer.
• Brush and saplings: heavy brushcutter line or a blade, on a trimmer rated for it.

Materials and Quality

Most trimmer line is nylon copolymer. Premium lines add reinforcing cores or blended materials to resist breaking and welding. Welding is when line fuses inside the spool from heat, common on cordless trimmers run hard on hot days. Cheaper line can be brittle, especially once it dries out. Storing spare line in a sealed bag, or soaking dry line in water overnight before winding, restores some flexibility. When you are ready to choose a specific product, our best trimmer line roundup compares current options by diameter and shape.

Fit Problems and How to Fix Them

Line will not feed

Usually line that is too thick for the eyelets or the bump mechanism, line wound too loosely or crossed on the spool, or line that has welded from heat. Rewind tightly in the direction marked on the spool, and step down a size if the eyelets are tight.

Line breaks constantly

Too thin for the work, old and brittle, or you are hitting hard surfaces at full speed. Try one size up if the trimmer accepts it, switch to round or twisted near concrete, and approach edges with the tip of the line rather than burying the head.

Trimmer bogs down or battery dies fast

Line too thick or too long. Most heads have a cutoff blade on the guard that sets the correct length; do not remove it. Drop a size or switch from a heavy shaped line to a lighter twisted one.

How Much Line to Wind

Typical single-line spools hold about 15 to 25 feet, and dual-line heads often take around 10 to 15 feet per side, but this varies by head and diameter; thicker line fits less on the same spool. Overfilling stops the line from feeding. Our step-by-step guide to restringing a weed eater covers winding direction and how much to load. Fixed-line and speed-feed heads use pre-cut lengths or a pass-through design; follow the length guide on the head.

Head Type Changes the Answer

The same trimmer can behave differently depending on the head fitted to it, so it helps to know which type you have before buying line.

• Automatic or auto-feed heads: common on light electric trimmers. They advance line each time you release the trigger and are the fussiest about diameter. Use exactly the size listed; even one step thicker often stops feeding.
• Bump-feed heads: the most common on gas and battery trimmers. You tap the head on the ground to release more line. They usually accept a range, such as 0.065 to 0.080 or 0.080 to 0.095 inch.
• Speed-feed or load-through heads: you push line straight through the eyelets and twist the knob to wind it. Very convenient, but eyelet size limits the maximum diameter.
• Fixed-line heads: take pre-cut pieces, often thicker and shaped. They suit heavy weeds because short, thick line does not need to feed, but you stop to replace pieces as they wear.

Many aftermarket universal heads let you run heavier line on a gas trimmer, but check that the head fits your arbor thread and is rated for your engine before switching.

Edging vs Trimming

If you turn the trimmer vertically to edge sidewalks and driveways, line wears much faster because it constantly strikes concrete. Round or twisted line in the upper half of your trimmer’s range holds up best for this. Shaped line dulls quickly against hardscape and loses its advantage. If you edge a lot, a dedicated edger or edging attachment saves line and gives a cleaner cut; see string trimmer vs edger for when one makes sense.

Safety Notes

Never replace nylon line with wire, cable or metal-reinforced cord. It can break off and become a dangerous projectile. Keep the guard and its line-cutting blade in place, wear eye protection and long pants, and keep people and pets at least 50 feet away while trimming.

Buying Tips

• Buy the right diameter first; shape and brand are second.
• A medium spool (about 1 to 3 pounds) is enough for most homeowners for a season or two.
• Pre-wound replacement spools are convenient for cordless trimmers but cost more per foot.
• Keep a spare length of line in the trimmer bag for quick fixes.
• If you own trimmers from two brands, a size they both accept, often 0.080, simplifies buying.

For more on trimming technique and season-long yard routines, see our string trimmer how-to and the lawn care guide.