The Basic Steps for Replacing Trimmer Line

Replacing trimmer line takes about five minutes once you know where the spool is and how your trimmer's head releases. Most trimmers use one of two designs: a fixed spool that you unwind by hand, or a cartridge that twists out. You'll need fresh trimmer line (usually 0.080 or 0.095 inches thick, depending on your trimmer model), scissors, and sometimes a small screwdriver or hex key—check your trimmer's manual to see which.

The process is the same whether your trimmer is gas-powered, electric, or battery-operated: stop the engine or unplug it, locate the spool head, remove the old line, wind the new line onto the spool in the correct direction, and reassemble. The most common mistake is winding the line backward, which causes it to tangle or not feed properly when you restart.

Key Takeaways

  • Most trimmers have either a fixed spool you unwind by hand or a twist-off cartridge; your manual tells you which type yours is.
  • Wind new line in the direction marked on the spool head—usually counterclockwise when looking down at the head—or it will jam when you try to use it.
  • Cut the line to the length marked on your spool (usually 17 to 20 inches per side) before winding to avoid tangling and wasted line.
  • If your trimmer has a bump-feed head, you only need to replace one line; if it has a fixed head, you may need to wind two separate lengths.

Locate and Access the Spool Head

The spool head is the round part at the bottom of your trimmer where the line comes out. On most models, you'll see a small cap or cover in the center. Some trimmers have a screw or bolt holding this cap; others have a slot where you insert a screwdriver or hex key to turn it counterclockwise and release it. A few models use a straightforward twist-off design with no tools needed.

If you're unsure which type you have, check the manual or look for markings on the head itself. Once you've removed the cap, you'll see the spool underneath—a plastic bobbin or cartridge that holds the line. If the spool is a separate cartridge, twist it counterclockwise to unwind it from the head. If it's fixed in place, you'll unwind the line by hand in the next step.

Remove the Old Line and Clean the Spool

Pull out any remaining old line from the spool. If the line is wound tightly, you may need to turn the spool counterclockwise by hand to loosen it. Once the spool is empty, take a moment to wipe away any grass clippings, dirt, or dried line fragments with a dry cloth. A clean spool winds new line more smoothly and prevents jams.

Check the spool for cracks or damage. If the plastic is cracked or the grooves where the line sits are worn smooth, the spool may need to be replaced rather than refilled. Most hardware stores and online retailers sell replacement spools for common trimmer models for $10 to $25.

Measure and Cut Your New Line

Look for a line-length marking on the spool head or in your manual—this is usually between 17 and 20 inches per side. Cut two pieces of line to this length using scissors or a utility knife. Cutting to the correct length prevents the line from tangling as you wind it and stops you from wasting expensive line by overfilling the spool.

If you're not sure of the correct length, err on the side of slightly shorter rather than longer. A spool that's too full will jam when you try to feed the line; one that's slightly underfilled will work fine and straightforward need refilling sooner.

Wind the Line onto the Spool in the Correct Direction

This step is where most people go wrong. Look for an arrow or directional marking on the spool head—it will point either clockwise or counterclockwise. Wind your line in the direction the arrow points. If there's no arrow, the standard direction is counterclockwise when you're looking down at the spool from above.

Insert one end of your first line piece into the small notch or slot at the edge of the spool (most spools have one or two of these). Hold the line taut with one hand and turn the spool slowly with the other, wrapping the line around the spool in neat, overlapping coils. Don't let the line bunch up or cross over itself—each wrap should sit next to the previous one. Once the first piece is wound, insert the second piece into the other notch and wind it the same way. Leave about 4 to 6 inches of line sticking out from each notch so it will feed properly when you reassemble the head.

Reassemble the Spool Head and Test

If your spool is a removable cartridge, twist it clockwise back onto the head until it's snug. If it's a fixed spool, straightforward replace the center cap and tighten it by turning clockwise with your screwdriver or hex key. Don't overtighten—snug is enough, and over-tightening can crack the plastic.

Before you start the trimmer, hold it upright and gently tug on each line to make sure it feeds freely. The line should pull out smoothly without resistance. If it doesn't, the line is probably wound backward or too tightly. Stop and rewind it in the opposite direction. Once the line feeds smoothly, you're ready to use the trimmer. The line will trim to the correct length automatically as you work, either through a fixed cutting blade on the head or through a bump-feed mechanism if your trimmer has one.

Common Mistakes and How to Avoid Them

Winding backward: The line won't feed or will jam when ready. Check the arrow on your spool head before you start, and if you're unsure, wind a short test section, reassemble, and tug the line. If it doesn't pull out smoothly, unwind and try the opposite direction.

Overfilling the spool: Too much line packed onto the spool causes jams and prevents the head from closing properly. Stick to the marked line length and don't try to squeeze in extra. Crossing or bunching the line: Wrap each coil neatly next to the previous one. Crossed or bunched line will tangle and jam. Forgetting to leave line sticking out: If you wind the line all the way to the edge with nothing protruding, it won't feed when you reassemble. Leave 4 to 6 inches hanging out from each notch.

Frequently Asked Questions

What size trimmer line do I need?

Check your trimmer's manual or look for a marking on the spool head itself. The most common sizes are 0.080 inches and 0.095 inches in diameter. Using the wrong size can cause feeding problems or poor cutting. If you've lost the manual, the trimmer model number is usually stamped on the housing, and you can search online for the specs.

Can I use any brand of trimmer line?

Yes. Trimmer line is a commodity product—any brand in the correct diameter will work in your trimmer. Specialty lines (twisted, serrated, or thicker) may cut better on thick weeds, but standard round line works fine for most home yards and costs less.

How often do I need to replace the line?

It depends on how often you trim and what you're cutting. Light residential use might need a new spool every few months; heavy use or cutting thick weeds might need it every few weeks. You'll know it's time when the line becomes noticeably shorter or stops cutting cleanly.

What if the line won't feed after I reassemble the head?

The line is almost certainly wound backward. Unwind it completely and rewind in the opposite direction. If you're still unsure which way is correct, check for an arrow on the spool head or consult your manual. If the line feeds but when ready jams, you've overfilled the spool—remove some line and try again.

Do I need to replace the spool itself, or just the line?

Usually just the line. The spool is reusable and lasts for years. Replace the spool only if it's cracked, the grooves are worn smooth, or it won't stay seated in the head. A replacement spool costs $10 to $25 and is worth buying if your current one is damaged.