Eighteen inches is where a chainsaw becomes a felling tool rather than a log processor. A 45 cm bar reaches through most trees in a British garden or small woodland in one pass, and it needs a real engine behind it. We hold 26 models with a 45 cm (18 inch) bar.
- What it cuts: trunks and logs up to about 40 cm in a single pass.
- Power it needs: 50 cc and upwards on petrol; this is beyond what mains saws and most batteries manage.
- Who it suits: felling, heavy cross-cutting, storm clearance and anyone working with timber rather than garden waste.
It is too much saw for pruning and garden tidying: heavier, more tiring, and more bar than you can safely control one-handed. For those jobs, 12 or 14 inches is the better tool.
18 inch chainsaws compared
Current models on file at this bar length, across petrol, battery and mains.
How much wood a 18 inch bar really handles
The usable cutting length is the number quoted, measured from the saw body to the bar tip, so a 45 cm bar cuts a log of about 45 cm in one pass. The practical working rule is to choose a bar around 5 cm longer than the thickest wood you cut regularly, which puts this size at its best on timber up to roughly 40 cm.
Thicker logs are not impossible: cutting from both sides doubles the effective capacity. It is slower, and on a felling cut it makes an accurate hinge harder, which is why felling wants a bar longer than the trunk rather than a technique that works around a short one.
Matching the engine or motor to the bar
A 45 cm bar needs 50 cc or more on petrol to keep chain speed up in a full-depth cut. Saws such as the Husqvarna 450 and the Stihl MS 261 and MS 291 sit here. Mains saws effectively stop before this length because a 13A socket cannot supply the power, and only the largest battery platforms, 60V and 80V, reach it. Expect a dry weight of 5 to 6 kg before fuel and bar, which you will feel by the end of a session.
An underpowered saw with a long bar is the most common bad buy in this market: it cuts slowly, loses chain speed in the cut, and wears the drive sprocket. Manufacturers list permitted bar lengths per model for exactly this reason, and fitting a longer bar than the list allows usually voids the guarantee.
Chains and files for this size
At 45 cm you are usually on 0.325 inch or full 3/8 inch chain, filed with a 4.8 mm or 5.2 mm round file respectively, with a 1.3 mm or 1.5 mm gauge. Full 3/8 inch chain is more aggressive and suits the bigger engines. Keep the depth gauges filed down as the cutters shorten, or a long bar will simply ride on the wood.
Three numbers buy a chain: the cutting length, the pitch and the gauge, plus the drive link count. All of them are usually stamped on the bar near the saw body. Chain length is not interchangeable between saws of the same bar length, because drive link counts differ.
One size up, one size down
Step down to 16 inch if firewood rather than felling is the main job, and you will save weight and money. Step up to 20 inch for larger trunks and milling.
If you are still deciding on power rather than length, compare the petrol, cordless and corded ranges.
18 inch chainsaw FAQs
What size engine does an 18 inch chainsaw need?
50 cc or more. Below that the saw will physically carry a 45 cm bar but will bog in a full-depth cut, wear the clutch and sprocket and cut slowly enough to be frustrating. Manufacturers publish permitted bar lengths per model, and on a saw this size that list is worth following exactly.
Is an 18 inch chainsaw too big for home use?
For garden work, yes, usually. It is heavier, harder to control and more saw than branches and logs require. If you fell trees on your own land or process whole trunks, it earns its place. Many people are better served by a 16 inch saw for firewood and a small battery saw for pruning.
How do you measure a chainsaw bar?
Measure from the point where the bar leaves the saw body to the tip, then round to the nearest standard size. That gives the cutting length, which is what "18 inch" means here and on the packaging. The whole bar is longer, because part of it is clamped inside the saw, so measuring the bar on its own gives a number that does not match anything you can buy. A 18 inch bar is 45 cm.
Can you put an 18 inch bar on a smaller saw?
Only if the manufacturer lists it for that model. The bar mount may well fit, which is what tempts people, but an underpowered saw with a long bar cuts slowly, overheats the clutch and generally voids the warranty. You also need the right chain for the new drive link count.
How tight should the chain be?
Tight enough that the drive links stay in the bar groove when you pull the chain away from the bar, loose enough to turn it round the bar by hand with a glove on. Check it cold, and again after the first few cuts with a new chain, because chains stretch as they bed in. A chain that keeps coming off is usually too loose or running on worn bar rails.
