What Size String Trimmer Do I Need? Match Swath, Power and Weight to Your Yard

The right size of string trimmer is the lightest one whose cutting swath, power and shaft still clear your edges, your growth and your height. I size a trimmer by the length of edge it has to work, because the mower handles the open lawn and the line works along fences, beds and trunks. On my quarter-acre house lawn the trimmer touches only beds, walks and the work pad, while the orchard fence lines and the ditch bank bring tall growth. Below I sort string trimmer size into swath, power, weight and reach, work one fence strip through with maker figures, and finish with a fit check.

What Size String Trimmer Do I Need? Start With Edges and Growth

Start with two facts about your property: how much edge you trim and how tall and thick the growth gets. Edge length and growth decide the size, and the area of the lawn matters little, since a mower covers the open grass. The table sorts common jobs into three size classes. If your job is a cut-in border rather than trimming, my guide on what size edger you need uses the same edge-first logic.

The classes overlap on purpose. Your height and the thickest growth you meet can move you one class up or down, and the four checks below show how. Power source and the battery or fuel routine come after the class, because the maker’s own manual sets what each head can cut.

The Four Sizes That Matter on a String Trimmer

A trimmer has four sizes that change how it works in your hands: the cutting swath, the power class, the weight and the shaft. Makers print the first three on the box and often leave the fourth out.

Cutting Swath

The swath is the circle the line draws, and the maker’s number belongs to a line at its proper length. Makers print 13 in on smaller battery models and 17 to 19 in on gas models. Some let you choose. I map swath to individual yards in a separate look at string trimmer cutting width.

According to DeWalt, the DCST972X1 swath adjusts between 15 and 17 in, and Milwaukee sets 14 or 16 in on its M18 kit by turning the line cut-off blade 180 degrees. Greenworks tells owners in its manual to set 14 in for greater run time and 16 in for a larger cutting area.

Along the tree-row strips I match the swath to the width of the strip, so one pass lands on the edge of the grass and the line stays off the trunk bases. EGO warns in its manual that tree bark, wood moldings and fence posts are easily damaged by the line, so a wide swath near young trunks costs you bark.

Power Class in Volts, Amp-Hours and Engine Size

Gas engines are rated in cubic centimeters, battery tools in volts and amp-hours, and corded tools in amps. None of these converts into another, so no box can honestly rank a 28 cc engine against a 56V pack on cutting power. Voltage names add confusion: DeWalt prints 60V for a pack it says has a nominal voltage of 54, so a higher number on the label does not always mean a stronger pack. If you are choosing between packs, I compare 40V and 56V string trimmers side by side.

What I read instead is the line the head accepts. DeWalt lists 0.080 in line for the DCST972X1 and also accepts 0.095 in, and EGO lists 0.095 in for the ST1623T. The line diameter the head accepts is one selection factor, next to the jobs the maker names for the tool, and it never ranks one motor against another.

Weight You Carry

Weight is the size you feel after the third edge, and the first edge hides it. The figures are not on the same footing: a gas maker leaves out the cutting head, the guard and the fuel, and a battery maker may or may not count the pack, so ask what the number includes before you compare two trimmers. I list the stated weights of lighter models in my lightweight string trimmer picks.

Vibration is a separate handling concern. In a laboratory test of grounds-maintenance tools, gloved hand vibration was 3.5 to 5.8 m/s2 for a grass trimmer against 1.1 to 2.0 m/s2 for a backpack blower, and the trimmer gave the highest exposure of the tools tested (1). After a long edge along the gravel yard my hands tell me more than the box does, so I stop for a break before they go numb and I switch grip often.

Shaft Length and Your Height

Many makers do not publish a shaft length, so test it yourself. Both EGO and Husqvarna say to hold the line parallel to the ground, and EGO says never to operate the machine above waist height. Stand upright and hold the trimmer the way the manual shows, with the head at cutting height and the line parallel to the ground. Shaft shape changes reach and posture too, which I cover in straight and curved shaft trimmers.

If you have to stoop to get the head down, that has a cost. A posture study of young agricultural workers using a brushcutter measured a trunk lean of about 34 degrees, and its authors called for prevention of musculoskeletal disorders (2). A brushcutter is a different machine, but the lesson carries over: choose a telescoping or adjustable shaft if you are tall, and a lighter compact model if you are short.

Worked Example of Sizing a Trimmer to One Fence Strip

Take a 100 ft fence run with a strip of rank growth 4 ft wide, the kind of strip I meet at the orchard fence lines. The swath decides how many passes you make across the strip.

The 16 in swath saves one pass in four and about 100 ft of walking. These counts are idealized: they assume full-width cutting with no overlap between passes, and real passes overlap a little.

The wider swath has a cost on a battery model. Greenworks says in its manual to set 14 in for greater run time and 16 in for a larger cutting area, so I plan the strip around the pack and count a second pack as part of the trimmer. I compare the two models in my guide to Greenworks 60V and 80V trimmers.

Size Table of Maker Figures for Swath, Power and Weight

This table shows the spread across the classes, using one example for each. The weight cells carry the maker’s own wording, because the numbers leave out different parts.

Read across the rows and the pattern is plain: the swath grows from 14 in to 18 in, and the gas models are the heaviest even before you add fuel, the head and the guard. A battery model that lists no weight, like the DeWalt, is a reason to hold it in a shop before you buy.

When a Bigger Trimmer Is the Wrong Size

A larger swath or a larger engine can add weight, so the biggest trimmer is the wrong one for edges that a smaller tool clears. Two costs deserve a number.

Noise and Fumes From Large Gas Models

Two grass-trimmer engines measured at the operator gave about 100 and 105 dB(A), above the ISO, NIOSH and OSHA limits for an 8-hour day (3). A study of landscape workers found significantly more noise and carbon monoxide exposure with fuel-powered trimmers than with battery versions (4). On the house lawn that is why I reach for a battery model, as I explain in battery and gas string trimmers, and I wear ear protection on every tool, whatever the type.

A gas trimmer never runs in a shed or a garage, even with the door open. I refuel outdoors with the engine off and cool, and I move away from the fuel spot before I start it.

Line Length Is Not a Bigger Swath

Some owners try to gain swath by letting the line grow. The manuals say no: EGO and Craftsman tie extra line to motor overheating, and DeWalt says line past the swath you have set harms performance, run time and motor life. A laboratory test that varied line length, engine speed and handle material found its lowest hand vibration, 2.76 m/s2, with a 100 mm line (5). The guard blade trims the line to the maker’s length for a reason, so buy the swath you need instead of growing it.

Safety Gear and Distance Scale With the Size

Every trimmer throws debris, so gear and distance come with the choice, whatever the size. CPSC injury data analyzed in a US study estimated 81,907 lawn trimmer injuries treated in emergency departments from 2000 to 2009, and the eye accounted for 42.5 percent of them (6). I wear eye protection that meets ANSI Z87.1, hearing protection, gloves, heavy long pants, long sleeves and sturdy slip-resistant boots every time, as the maker manuals ask.

Keep people and pets away by the distance in your manual. EGO, Echo and Husqvarna give 50 ft (15 m), while DeWalt and Craftsman give 100 ft (30 m), and I stop the tool when someone walks closer.

Woody stems and brambles belong to a brush cutter, not a trimmer head, a split I explain in string trimmers and brush cutters. Cut them only with a blade the maker approves for woody growth, within its stated stem size, on a tool whose maker lists that blade, guard, handle and harness. A grass blade does not cut wood, and fitting a metal blade to a trimmer that is not rated for one is never a way to size up.

Five Checks Before You Buy

Choose a string trimmer with five checks, and you can make all of them before you pay. I run through them in this order, and the first two cost nothing.

1. Walk your edges and note the thickest growth. Write down the longest fence run and the tallest weeds. For the tallest growth, I pick nine models in my roundup of string trimmers for tall grass.
2. Pick the size class from the first table and read the maker’s swath for the model, including any adjustable setting.
3. Hold the trimmer with the battery fitted or the tank empty. Stand upright and check that you can keep the head at cutting height with the line parallel to the ground, as the manual shows.
4. Read the line diameter in the manual and the swath limit it sets. Buy only line the manual lists for that head. My guide on which trimmer line to use starts from your manual.
5. Count the packs or the fuel routine. A battery model needs a spare pack only when the work runs longer than one charge or must not stop, and every pack and charger must be the ones the maker approves for that exact tool, charged and stored within the temperature range in the manual and never used if damaged or swollen. For a gas model, use only the fuel, oil and lubrication routine in the manual for that exact model, since a two-stroke and a four-stroke can differ.

Buy the Lightest Trimmer That Clears Your Growth

Three points to remember: size the trimmer to your edges and growth, read what each weight figure includes, and plan battery capacity around the work you do. My own tip is to pace out the longest strip before you shop, because that one number tells you the class faster than any chart. Next, compare the models in your class on swath, line and weight, and set the swath the manual allows. Pick your string trimmer size from the edges you cut and the height you stand, and the lightest model that clears your growth is the right one. Once you know your class, my top string trimmer picks show models in each one.

Frequently Asked Questions

What are the important features and specifications to consider when buying a string trimmer?

The important specifications on a string trimmer are the cutting swath, the power source and its rating, the weight and what that weight includes, the line diameter the head accepts and the shaft length. The swath sets how much grass one pass covers, and the line diameter shows what the motor was built to turn. For a battery model, add the pack’s amp-hours and the platform it belongs to.

What size weed eater do I need?

The weed eater size you need follows your edges and your thickest growth: a compact class for beds and walks, a mid class for fence lines and tree bases, and a large class for long runs and tall weeds. Check the swath for the model, the line its head accepts and the weight with the battery fitted. Your height can move you one class up or down.

How to choose a cordless string trimmer?

To choose a cordless string trimmer, match the swath and the line the head accepts to your growth, then check the battery. Makers rate packs in volts and amp-hours and list run time at stated speeds, so compare packs inside one maker’s platform and add a spare pack only when the work runs past one charge. Hold the model with the battery fitted to judge its weight.

What is the best string trimmer for a short person?

The best string trimmer for a short person has an adjustable or telescoping shaft and a weight you can hold with the battery fitted, so the head sits at cutting height without reaching. The manuals say to hold the line parallel to the ground, and EGO says never to work above waist height. Try the model in a shop before you buy it.

Which weed trimmer can handle heavy weeds?

A weed trimmer handles heavy weeds when its head takes the line its manual lists and its swath suits the strip. EGO’s manual says to cut grass over 8 in from the top down in small steps, to avoid line wear and motor drag. Woody stems and brush belong to a brush cutter with a blade the maker approves for woody growth, within its stem limits, plus the guard, handles and harness listed for that tool.

References

1. Oh J, Chen N, Boyd C. Laboratory evaluation of occupational exposure to hand-arm vibration (HAV) during grounds maintenance equipment operations. Ann Agric Environ Med. 2023;30(2):384-389.
2. Roggio F, Vitale E, Filetti V, Rapisarda V, Musumeci G, Romano E. Ergonomic evaluation of young agricultural operators using handle equipment through electromyography and vibrations analysis between the fingers. Saf Health Work. 2022;13(4):440-447. doi:10.1016/j.shaw.2022.07.003
3. Mallick Z, Badruddin IA, Khaleed Hussain MT, Salman Ahmed NJ, Kanesan J. Noise characteristics of grass-trimming machine engines and their effect on operators. Noise Health. 2009;11(43):98-102. doi:10.4103/1463-1741.50694
4. Alexander BM, Graydon PS, Pena M, Feng HA, Beamer BR. Hazardous exposures and engineering controls in the landscaping services industry. Journal of Occupational and Environmental Hygiene. 2025;22(3):189-202.
5. Mallick Z. Optimization of the operating parameters of a grass trimming machine. Appl Ergon. 2010;41(2):260-265. doi:10.1016/j.apergo.2009.07.010
6. Leinert J, Griffin R, Blackburn J, McGwin G. The epidemiology of lawn trimmer injuries in the United States: 2000-2009. J Safety Res. 2012;43(2):137-139. doi:10.1016/j.jsr.2012.03.001

Safety Note: Read your manual first. A string trimmer or brush cutter throws debris with force, so clear stones, glass and wire from the area before you cut. Wear impact-rated eye protection with side coverage that meets ANSI Z87.1, hearing protection, gloves, heavy long pants, long sleeves and sturdy slip-resistant boots (steel-toe where your manual says so). Keep people and pets at least as far away as your manual says (50 feet in some manuals, 100 feet in others), and stop if anyone comes closer. Keep the correct guard fitted, use only the cutting attachments, handles and harness the maker approves for your exact tool, and never replace trimmer line with wire. A blade can kick sideways when it hits a stump or a thick stem, so fit the handlebar and harness your manual requires for blade work, hold both handles firmly and keep secure footing. Before you clear a jam, clean the tool or change line, a blade or an attachment, switch it off, wait for all movement to stop, then remove the battery, unplug the cord or disconnect the spark plug wire. Refuel a gas model outdoors with the engine off and cool, away from flames or sparks, and move away from the fueling spot before starting, as far as your manual says (often 10 to 30 feet); never run it in a garage, shed or other closed space. For a battery model, use only the maker’s battery and charger, charge it within the temperature range in your manual and never use a damaged or swollen pack. For a corded model, use a GFCI outlet, keep the cord clear of the cutting line and avoid wet conditions.