Walk into any tool shop and ask for a chainsaw, and the first question you’ll get is: “What size do you need?” If you don’t have a confident answer, you’ll probably end up with whatever the sales assistant fancies shifting that week — and that’s how you end up with a 20-inch petrol beast when all you needed was a compact battery saw for pruning.
Choosing the right chainsaw size matters more than most people realise. Too small and you’ll be fighting through every cut, overworking the motor and wearing out chains in record time. Too large and you’ve got an unwieldy, dangerous machine that’s overkill for the job. This guide walks you through exactly what size chainsaw you need based on what you’ll actually be using it for.
Understanding Chainsaw Sizing (Bar Length and Engine CC)
When people talk about chainsaw “size,” they’re usually referring to two things: bar length and engine power. Both matter, but bar length is the primary sizing metric.
Bar length is the measurement of the cutting bar from tip to where it enters the housing. It determines the maximum diameter of wood you can cut in a single pass. Common domestic sizes range from 10 inches up to 20 inches, though professional saws go much larger.
Engine power is measured in cubic centimetres (cc) for petrol models, or voltage/amp-hours for battery and electric models. More power means the chain can maintain speed through tougher cuts — but it also means more weight.
| Bar Length | Typical Engine Size | Weight Range | Best For |
|---|---|---|---|
| 10–12 inch | 25–35cc / 18V–36V battery | 2.5–4 kg | Pruning, light trimming, small branches |
| 14–16 inch | 35–45cc / 36V–56V battery | 4–5.5 kg | Firewood, medium trees, general garden work |
| 18–20 inch | 45–60cc | 5–7 kg | Large tree felling, thick trunks, heavy-duty work |
| 20+ inch | 60cc+ | 6–8+ kg | Professional forestry, very large trees |
Key point: A bigger bar doesn’t automatically mean better. A 20-inch bar on a weak engine will bog down constantly. You want the bar length matched to the engine power — reputable manufacturers get this balance right out of the box.
Electric vs Petrol vs Battery Chainsaws
Before you settle on a bar length, you need to decide on a power source. Each has genuine trade-offs.
Corded electric chainsaws are the lightest and cheapest option. They’re quiet, start instantly, and need minimal maintenance. The downside? You’re tethered to an extension lead, which limits range and can be a safety hazard. Best for occasional garden pruning near the house. Typically available in 10–16 inch bars.
Battery chainsaws have improved enormously in the last five years. Modern 36V and 56V models can genuinely compete with mid-range petrol saws for most domestic tasks. They’re quieter, lighter, and don’t produce fumes — brilliant if you’re working near the house or have neighbours close by. Run time is the main limitation: expect 30–60 minutes per battery depending on the work. Available in 10–16 inch bars, with some higher-end models reaching 18 inches.
Petrol chainsaws remain the go-to for serious cutting work. They offer the most power, longest run times (limited only by the fuel tank), and are available in every size. The trade-offs are weight, noise, fumes, and maintenance — you’ll need to mix two-stroke fuel, clean air filters, and they can be temperamental to start. For occasional homeowner use, a battery model may serve you better. For regular firewood cutting or tree felling, petrol is still king.
Chainsaw Size Guide by Task
Here’s the practical bit — what size chainsaw do you actually need for the jobs you’ll be doing?
Pruning and Light Trimming (10–12 inch)
If your main use is cutting back branches, tidying hedgerow growth, or trimming small trees, a 10–12 inch bar is plenty. These compact saws are light enough to use one-handed on a ladder (though I’d always recommend two hands for safety), and they’ll zip through branches up to about 20cm diameter without breaking a sweat.
A battery-powered model in this size range is ideal. You’ll get enough run time for a full afternoon of pruning, and the light weight means you won’t be exhausted after an hour.
Typical cuts: Branches up to 20cm, hedge trimming, storm damage cleanup (small branches), cutting Christmas trees.
Firewood and Medium Trees (14–16 inch)
This is the sweet spot for most homeowners. A 14–16 inch chainsaw handles firewood cutting, taking down small-to-medium trees (up to about 30cm diameter in a single pass), and general property maintenance. If you only own one chainsaw, this is the size to get.
At this size, you’ve got a genuine choice between battery and petrol. If you’re cutting a few logs every weekend for a wood burner, a battery model is convenient and capable. If you’re processing large quantities of firewood or cutting harder woods like oak and ash regularly, petrol gives you the sustained power and run time.
Typical cuts: Firewood logs, trees up to 30cm diameter (single pass) or 60cm (two opposing cuts), fence posts, thick branches.
Large Tree Felling (18–20+ inch)
If you’re felling large trees, cutting up storm-damaged trunks, or processing hardwood in serious quantities, you need an 18-inch bar or larger. These are almost exclusively petrol-powered at meaningful price points, and they’re significantly heavier and louder than smaller saws.
An honest note: If you’re not experienced with chainsaw work, felling large trees is genuinely dangerous. A tree falling the wrong way can kill you or destroy property. For trees over about 30cm diameter, I’d strongly suggest hiring a qualified tree surgeon unless you’ve had proper training. The chainsaw isn’t the hard part — knowing where and how the tree will fall is.
Typical cuts: Trees over 30cm diameter, large trunk sections, milling planks (with a guide), clearing large storm damage.
The Golden Rule — Bar Length vs Tree Diameter
There’s a simple rule that makes sizing straightforward:
Your bar length should be at least 2 inches longer than the diameter of what you’re cutting.
So for a 12-inch diameter trunk, you want at least a 14-inch bar. This gives the chain enough room to pass fully through without the tip binding in the cut.
You can cut larger diameter wood than your bar length by making two cuts from opposite sides. A 16-inch bar can handle a 28-inch trunk this way. But it’s slower, requires more skill to align the cuts, and increases the risk of the chain pinching. It’s a useful technique to know, not a reason to buy a smaller saw than you need.
| Tree/Log Diameter | Minimum Bar Length (Single Cut) | Minimum Bar Length (Double Cut) |
|---|---|---|
| Up to 20cm (8″) | 10 inch | — |
| 20–30cm (8–12″) | 14 inch | 10 inch |
| 30–40cm (12–16″) | 18 inch | 12 inch |
| 40–55cm (16–22″) | 24 inch | 16 inch |
| 55cm+ (22″+) | Specialist bar | 18–20 inch |
Safety Equipment You Must Have
I’m putting this high up because it’s non-negotiable. Chainsaws are one of the most dangerous power tools you can own. The chain moves at around 20 metres per second — it can cut to the bone before your brain even registers what’s happened.
You must have all of the following before you make your first cut. This isn’t optional, and it isn’t an area to buy the cheapest thing you find.
Chainsaw Chaps/Trousers
Chainsaw trousers (or chaps that go over your normal trousers) contain layers of fibrous material that jam the chain and stop it within fractions of a second if the saw contacts your leg. This is the single most important piece of safety kit. A chainsaw to the thigh without protection can be fatal — with chainsaw trousers, you’ll likely walk away with a bruise.
Look for trousers rated to Class 1 (20 m/s) at minimum. For most domestic chainsaws, this is sufficient. Professional users should look at Class 2 or 3.
Helmet with Visor and Ear Protection
A proper forestry helmet combines a hard hat (for falling branches), a mesh visor (for flying debris), and ear defenders (chainsaws are loud enough to cause hearing damage within minutes). You can buy all three separately, but an integrated helmet is cheaper, more convenient, and ensures everything stays in place.
Cut-Resistant Gloves
Chainsaw gloves have cut-resistant material across the back of the left hand (where kickback injuries most commonly occur). They also improve your grip, which reduces fatigue and increases control. Standard gardening gloves are not adequate.
Additional safety essentials:
- Steel-toe boots with chainsaw protection — proper chainsaw boots have cut-resistant layers like the trousers
- First aid kit — always have one accessible when using a chainsaw
- Never work alone — if something goes wrong, you need someone who can call for help
My Top Chainsaw Picks by Size
Based on my experience and research, here’s what I’d recommend at each size bracket:
Best Small Chainsaw (10–12 inch) — For Pruning and Light Work:
Look for a battery-powered model in the 18V–36V range. It should weigh under 4 kg with the battery, have a tool-free chain tensioner, and come from a battery platform you already own (or plan to invest in). At this size, brand battery ecosystems matter more than the individual saw — buying into a platform means the batteries work across all your garden tools.
Best Medium Chainsaw (14–16 inch) — The All-Rounder:
This is where you have the most choice. For occasional use (a few times a month), a 36V–56V battery model is genuinely excellent — clean, quiet, and powerful enough for firewood and small trees. For heavier use, a 40–45cc petrol saw gives unlimited run time and more consistent power through hardwood.
Best Large Chainsaw (18–20 inch) — For Serious Work:
At this size, petrol is the practical choice. Look for a 50–60cc engine, an anti-vibration system (your hands will thank you), and a reliable brand with good parts availability. Husqvarna, Stihl, and Echo dominate this space for good reason — their build quality and dealer support are noticeably better than budget brands.
Don’t forget the consumables:
- Bar and chain oil — the chain needs constant lubrication. Never run a chainsaw without it.
- Spare chains — chains dull, especially if you hit dirt. Having a spare means you’re not stuck mid-job.
- Chain sharpening kit — a round file and guide is cheap and extends chain life significantly. Sharpening a chain takes 10 minutes and makes a massive difference to cutting speed.
Final thought: If you’re unsure between two sizes, go for the smaller one. A chainsaw that’s too big is harder to control, more tiring to use, and more dangerous. You can always upgrade later once you know what you actually need — and a smaller saw will still be useful for lighter jobs even after you buy a bigger one.
