The type of motor: petrol (2-stroke or 4-stroke), electric (corded) or cordless (battery powered).

We recommend petrol line trimmers that score at least 85% overall, 85% for performance and 75% for ease of use, and electric or cordless battery models that score at least 80% overall, 75% for performance and 85% for ease of use.

This overall score is made up of performance (50%) and ease of use (50%).

We test by horizontally trimming along fences, walls and areas of lawn and vertically, with the cutting head perpendicular to the ground, along the edges of paths and garden borders. We also cut long grass up to 45cm high.

We assess how comfortable the trimmers are to use, taking into account their weight, balance, handles, angle of the cutting head and so on. Respooling the line, using controls, starting, using the line feed and vibration are also taken into account.

We assess how well the trimmer cuts with the head in a vertical position, such as when trimming along edges.

We assess how well the trimmer cuts with the head in a horizontal position, such as when cutting long grass or trimming the lawn.

We assess how well the trimmer cuts long grass up to 45cm tall.

How comfortable the handles are to reach, adjust and hold.

How the shaft length rates: just right, too short or too long, and whether it's adjustable.

How heavy the trimmer feels in use. Models that feel light and easily manageable score best.

How balanced the trimmer feels in use. A trimmer can be heavy but feel well-balanced, or lightweight yet unbalanced, for instance.

How easy it is to trim edges (i.e. vertical trimming). On some models the guard on the head can block your view, making it harder to trim accurately.

How well labelled and conveniently accessible the controls are. We look at the trigger, on/off switch, choke and primer (where applicable).

We assess whether the trimmer vibrates too noticeably or uncomfortably in use. All vibrate at least a little, but some can vibrate a lot and be uncomfortable to use for more than a few minutes.

How easy the trimmer is to start. Electric and cordless models are generally very easy, but petrol models usually use a starter cord and on some models this can take a fair bit of effort or several pulls to start.

How easy it is to feed out more cutting line in the head. Most models just need to be bumped on the ground so the line feeds out easily, some even feed out new line automatically, but some require you to do it manually.

How easy it is to put new cutting line (or blades) into the line spool in the trimmer head.

For cordless models, how many minutes the battery lasts with the trimmer constantly running.

The noise of the trimmer in decibels at the user's position and 7.5 metres away.

The year we tested this model. Tests from 2019 and onward are not comparable to earlier tests, due to a change in the test site.

Recommended retail price. This includes battery and charger for cordless models, but cordless models may also be sold without batteries.

For cordless models, the voltage and type of battery.

For cordless models, the manufacturer's stated time in minutes needed to fully charge the battery.

Automatic: Feeds out more line as needed. Bump: Tap the head on the ground to feed out more cutting line. Manual: You have to feed out more line by hand. Some models also feed out more line at the press of a button on the handle.

Models with only one cutting line tend to be easier to respool, but may not perform as well as models with two cutting lines.

Petrol models: Motor size in cc and power in kW. Electric: motor power in Watts. Cordless models usually don't state the motor power but the voltage is an indicator of comparative power.

For 2-stroke petrol models, the recommended fuel to oil ratio.

The fuel mix we used in our test of petrol 2-stroke models.

The weight of the trimmer in kilograms (for cordless models this includes the battery).

The overall length of the trimmer in centimetres. For models with telescopic shafts, the minimum and maximum overall lengths are shown.

The wider the cutting diameter, the easier it is to trim large areas of grass.

The thickness of the cutting line in millimetres.

Stated country of manufacture, but components may be sourced from a variety of countries.

Curved shafts can be easier to use for general trimming jobs. Straight shaft models can be more heavy-duty and may have a longer reach.

Trims the line to length as it feeds out.

Protects you from flying clippings and debris, but can also obscure your view of what you're cutting.

Allows you to adjust the shaft length. Usually only available on electric or cordless models as their motor is in the head, so there's no drive shaft in the shaft.

Only on petrol models. A clutch stops the cutting head from spinning when the motor idles – this is safer while you're moving between areas.

Safety mechanism that prevents the trimmer being switched on accidentally. The lock-off switch must be pressed before the on/off switch can start the trimmer.

Makes the trimmer easier to carry and use, especially for long jobs.

A small wire, metal or plastic projection which stops the cutting line getting too close to and damaging trees or other obstacles. Also serves as an edging guide for vertical trimming.

A small wire, metal or plastic projection which helps you achieve a clean, straight edge when trimming vertically. Usually acts as a tree guard in horizontal trimming.

Other heads that can replace the trimming head, such as hedge trimmers, power saws or soil cultivators. Usually optional accessories not included with the trimmer.

The cutting head rotates, making vertical trimming more convenient.

Items supplied as standard with the line trimmer.

Other features worth noting such as available extra attachments.