What Size Line Does a Cordless String Trimmer Need?
Most cordless string trimmers run best on line between 0.065 and 0.080 inches thick, and many light 20V models are built around 0.065 inch line. Larger, higher-voltage models can take thicker line, such as the 0.095 inch line on the EGO 56V trimmer. The right size for your tool is the one printed in its manual or on the spool housing, so check that first.
EGO Power+ ST1502SABest overall
HortiHub HG0556-AORTwo batteries, light build
ALSO GO Weed trimmerLightest listed weightThe short rule for line diameter
Line diameter is the thickness of the cutting string, measured in inches or millimeters. Thin line spins easily and suits light grass. Thick line cuts tougher weeds but asks more from the motor and battery.
Cordless trimmers have limited power compared with gas models, so they tend to use thinner line. A common range for battery trimmers is 0.065 to 0.080 inches (about 1.65 to 2.0 mm). Going above what the maker lists can slow the head, drain the battery faster and strain the motor.
Match the line to your trimmer
Our spec data shows how much the recommended line varies by model. The goodjob 20V trimmer lists 0.065 inch line and weighs 3.5 lb. The EGO POWER+ ST1502SA is a 56V, 140 Wh model with a 15 inch swath, and it lists 0.095 inch line. That is a clear step up in line thickness, and it goes with a bigger battery and a heavier body at 7.4 lb.
Many other models on our list do not publish a line diameter. In that case, look in three places:
- The owner's manual, which usually names the exact diameter or a range.
- A label on the spool, spool cover or trimmer head.
- The maker's parts page for your model number, where replacement spools show the size they carry.
| Line diameter | Typical use | Fits best on |
|---|---|---|
| 0.065 in | Light grass, edging, trimming along fences | Light 20V class trimmers |
| 0.080 in | Thicker grass and general yard work | Mid-range battery trimmers if the maker allows it |
| 0.095 in | Tougher weeds and bigger jobs | Higher-voltage, larger-swath models such as the EGO 56V |
Why the manual beats a general chart
Line charts online are a good starting point, but the trimmer head decides what fits. Spool holes, line guides and the cutting-head design are made for a certain thickness. Thicker line may not feed through, and thinner line may break or feed too fast.
Auto feed heads add another limit. For example, the HortiHub 12 inch model advances line automatically and releases a short length at start. Its listing tells you to extend the line to 6 inches before first use. Systems like this depend on the spool and line the maker supplies, so swapping to a different thickness can cause feeding problems.
If your manual gives a range, start at the thinner end. Move up only if you keep running into tough weeds and the head still feeds smoothly.
Choosing the right trimmer size for your yard
Many people asking about line size are really asking what size trimmer to buy. Three specs shape that choice: battery energy, cutting swath and weight.
Battery energy is shown in Wh. The EGO lists 140 Wh, while the 20V units on our list list 40 Wh. A larger number generally means more work between charges. Swath is the width of the cut circle, and a wider one means fewer passes. Most models that list it show 12 in or 13 in, and the EGO's 15 in is the widest on our page. Weight runs from 3.28 lb to 7.8 lb among models that list it.
As a rough guide, a small yard with fences and garden beds suits a light 20V trimmer with a 12 inch swath. A larger yard, thick weeds or long sessions call for a bigger battery, a wider swath and thicker line. Our best cordless string trimmer page ranks these models side by side by specification, so you can compare them on one sheet.
How to change the line safely
Swapping line takes a few minutes, but a trimmer that starts by accident can injure you. Follow these steps:
- Remove the battery. Do not rely on the trigger lock alone.
- Open the spool cover, usually by pressing tabs or twisting it.
- Take out the old spool and clear out dirt and grass.
- Load new line of the size your manual lists, following the arrows or winding direction marked on the spool.
- Feed the ends through the line eyelets and refit the cover.
- Reinsert the battery only after everything is closed and clear.
Safety and care notes
Wear eye protection every time you trim. Line, stones and grit can fly off the head at speed. The HortiHub listing, for instance, includes goggles, and any trimmer benefits from them. Long pants and closed shoes help too. Cordless trimmers are quieter than gas models, but hearing protection is still sensible for long jobs or noisy surroundings.
Keep bystanders and pets well away while the head is spinning. Do not use line types the maker has not approved, and never replace string with wire or metal cord, which can break off and cause serious injury.
If line keeps breaking or the head feels sluggish, check that the diameter matches your manual, that the line is not old and brittle, and that you are not cutting against hard edges like concrete. Storing spare line away from heat and sun helps it stay flexible.
Frequently asked questions
Can I use thicker line to cut tougher weeds?
Only if your manual allows it. A thicker line adds drag on the head, which can drain the battery faster and overload a small motor. If you need more cutting power, a model built for thicker line is usually the better answer.
Is round line the only kind I can use?
No. Line also comes in shapes such as square or twisted, which can cut more aggressively. Check that the shape and diameter are both approved for your trimmer head.
How long should the line be?
Follow the length in your manual. Some trimmers need the line extended to a set length before use, like the 6 inches the HortiHub listing calls for, and a line cutter blade on the guard usually trims it to the right length.
Does the battery voltage tell me the line size?
Not directly, but higher-voltage models tend to handle thicker line. In our data, the 20V goodjob lists 0.065 inch line, while the 56V EGO lists 0.095 inch line.