The correct chainsaw file size depends on your chain's pitch: 3.2mm for 1/4" P, 4.0mm for 3/8" LP, 4.8mm for .325", 5.2mm for 3/8" Standard, and 5.5mm for .404". Using the wrong diameter creates a hook that grabs and dulls instantly, or files away the cutter's bite entirely.
You can have the most powerful Stihl MS 661 in the world, but if you touch it with a dull, clogged, or wrong-sized file, you'll just be making expensive noise.
A chainsaw file is a precision instrument. It determines the shape of your cutter, the speed of your cut, and the safety of your saw. Yet, most people treat them like scrap metal. In this guide, we break down the non-negotiables: exact sizing charts, how to handle them, and how to know when your file is dead.
Mastering the Basics: Once you have the right file, you need to know how to use it. Check out our comprehensive guide on how to sharpen a chainsaw chain by hand for the step-by-step technique.
The Critical Chart: Which File Size Do I Need?
The #1 reason people ruin their chains is using the wrong file diameter.
Too Small: You create a "hook" under the cutter. It grabs the wood, causes vibration, and dulls instantly.
Too Large: You file away the cutting edge and the hook. The saw won't bite; you have to lean on it to get it to cut.
Here is the definitive lookup table for Australian chains:
| Pitch | Common Saws | File Size (Metric) | File Size (Imperial) |
| 1/4" P | Carving Saws, Pole Saws | 3.2mm | 1/8" |
| 3/8" LP (Picco) | Stihl MS 170/180, 201T, Battery Saws | 4.0mm | 5/32" |
| .325" | MS 261, Husky 450, Farm Saws | 4.8mm | 3/16" |
| 3/8" Std | MS 462, MS 661, 60cc+ Saws | 5.2mm | 13/64" |
| .404" | MS 881, Harvesters, Slabbers | 5.5mm | 7/32" |
⚠️ The "Stihl" Trap: Be careful with .325 chain. Stihl often uses a 4.8mm file, while some Oregon/Carlton .325 chains prefer a 4.5mm file. Check the box your chain came in. When in doubt, 4.8mm is the industry standard for .325.
What Makes a "Good" File?
Not all steel is created equal.
Hardness: Good files are heat-treated to stay harder than the chrome cutter on your chain.
Consistency: The spiral cut of the teeth is uniform, giving you a smooth stroke rather than a "gritty" feel.
Pro Tip: If your file feels like it's "skating" over the tooth instead of biting into it, throw it away. You are polishing the chain, not sharpening it.
Handling: The "One Way" Rule
A chainsaw file is a single-cut tool. It is designed to cut in one direction only: the push stroke.
The Grip: Hold the handle firmly in your dominant hand. Use your other hand to guide the tip of the file.
The Stroke: Push forward with steady pressure.
The Return: Lift the file off the cutter on the way back. Never drag the file backwards — you will damage the file. Dragging it backwards rolls the fine teeth of the file over, dulling the file instantly, and clogs it with metal filings.
How to Clean a File (The Chalk Trick)
As you file, the grooves fill up with steel dust (swarf). A clogged file generates heat and stops cutting.
Tap it out: After every few teeth, tap the tip of the file on a block of wood to knock the dust loose.
The "Chalk" Hack: Before you start, rub some standard blackboard chalk over your file. The chalk fills the valleys, preventing oil and metal chips from sticking. It sounds messy, but it keeps the file biting for twice as long.
File Card: If it's really gummed up with oil, use a "File Card" (a stiff wire brush) to clean out the grooves. Stroke parallel to the spiral.
When is My File Dead?
A file is a consumable item, not a "lifetime tool." Using a dead file is dangerous because you have to apply excessive pressure to get it to work, which leads to slipping.
The "Slide Test": Hold the file lightly between two fingers and place it on the cutter. If it bites, it's good. If it slides, it's dead — bin it.
The Visual Check: Look at the file under a light. A sharp file looks dull matte grey; a dead file looks shiny (the teeth have rounded over and are reflecting light).
Chainsaw File Size — FAQ
What size file do I need for a 3/8 LP chain?
4.0mm (5/32 inch). This is the common size for Stihl MS 170/180, the 201T and most battery saws.
What size file do I need for a .325 inch chain?
4.8mm (3/16 inch) in most cases, though some Oregon and Carlton .325 chains use 4.5mm. Check the packaging your chain came in if unsure.
How do I know if my chainsaw file is worn out?
Hold it lightly against a cutter. If it bites, it's still good. If it slides without cutting, it's dead and should be replaced — continuing to use it just polishes the chain rather than sharpening it.
Can I drag the file backward on the return stroke?
No. A chainsaw file only cuts on the push stroke. Dragging it back rolls the fine teeth over, dulling the file and clogging it with metal filings.
Ready to put that fresh file to work? Jump over to our master guide on how to sharpen a chainsaw chain by hand, or step up to the advanced filing and depth gauge protocol. And if a chain is worn past filing, replace it with one matched to your saw — Search by Chainsaw or Search by Bar Stamp.
Need the right chain for your saw?
Don't guess — match it exactly. Read the pitch, gauge and drive-link count off your bar and we'll find your precise chain, or search by your saw model. Every chain is backed by our Guaranteed Fit promise, checked against your bar stamp before it ships.