You can fit a longer bar only if your saw’s maker lists that length for your saw. Makers publish approved bar and chain combinations: Husqvarna says its 445 II and 450 II meet the EN ISO 11681-1 chainsaw safety requirements when fitted with the guide bar and chain combinations listed in the manual, and its manuals tell owners to use only approved combinations. We found no general “one size up” rule in the maker sources we checked.
Makita, for example, gives a recommended guide bar length of 300–400 mm for its DUC353 and DUC405 and 300–450 mm for its UC3551A corded saw, and says in the UC3551A manual that it accepts no responsibility for accidents or damage if non-approved bars or saw chains are used.
How Far Can You Safely Upsize Your Chainsaw Bar?
Use only the bar lengths listed for your saw. Stihl, for example, lists 30, 35 and 40 cm bars for the MS 170 and 30 to 45 cm for the MS 250, and Husqvarna lists 14, 16 and 18 inch bars for the 235, 236 and 240.
We have not found maker data on how oil delivery or engine load changes with bar length, so we give no reason beyond the maker’s approval.
Husqvarna’s 445 II and 450 II manual also links kickback to the bar nose: it says that for a given bar length you can use a guide bar with a smaller nose radius than the one listed.
Maximum Bar Lengths by Saw Size
Bar lengths makers list for some saws (from their manuals and product pages):
| Saw | Bar lengths listed by the maker | Notes |
|---|---|---|
| Stihl MS 170 | 30, 35, 40 cm | 3/8″ P 1.1 mm chain only |
| Stihl MS 250 | 30–45 cm (3/8″ P) or 35–45 cm (.325″) | Two pitches listed |
| Stihl MS 500i | 40–90 cm | 3/8″ 1.6 mm |
| Stihl MSA 220 C (battery) | 30–40 cm | 3/8″ P |
| Husqvarna 235, 236, 240 | 14, 16, 18″ | 3/8″ mini 1.3 mm |
| Husqvarna 340i (battery) | 12, 14, 16″ | 3/8″ mini 1.3 mm |
| Makita DUC353 / DUC405 (battery) | 300–400 mm recommended | 2 × 18 V |
| Makita UC3551A (corded) | 300–450 mm recommended | 3/8″ 1.3 mm |
| Milwaukee M18 FCHS (battery) | 40 cm | The 35 cm version is sold as the M18 FCHS35 |
Recommended Chainsaw Chains
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Always check your manual. The bar lengths approved for your saw are in its technical data. If the longest bar listed is 16 inches, don’t fit an 18-inch bar.
What Changes When You Fit a Longer Bar?
When you fit a longer bar:
- Chain length increases. A longer bar needs more drive links: Stihl lists 50 drive links for a 35 cm and 55 for a 40 cm 3/8″ P bar, and 56 and 62 for .325″ 1.6 mm Rapid Super at 35 and 40 cm. Buy a chain with the right count.
- Kickback zone. Husqvarna says kickback happens when the kickback zone at the nose of the guide bar touches an object.
- Approval. Husqvarna says its 445 II and 450 II meet the EN ISO 11681-1 chainsaw safety requirements when fitted with the guide bar and chain combinations listed in the manual; a length that is not listed is outside that approval.
What About Fitting a Shorter Bar?
A shorter bar is fine only if your manual lists that length. You’ll need a chain with fewer drive links, and the bar must suit your saw’s bar mount: Oregon bar codes include a mount code (for example A041 in 160SDEA041), so check the mount as well as the pitch and gauge.
The trade-off is that a shorter bar cuts a smaller diameter in one pass.
Battery Chainsaws — Can You Upsize the Bar?
Only within the lengths the maker lists. Some battery saws are approved for more than one length — Makita gives 300–400 mm for the DUC353 and DUC405, and Stihl lists 30–40 cm for the MSA 220 C — while others are sold as separate models for each length (Milwaukee’s M18 FCHS is 40 cm and the M18 FCHS35 is 35 cm).
We have no maker data on battery runtime with a longer bar. Use only the lengths in your manual.
Safety Risks of Oversizing Your Chainsaw Bar
Fitting a bar that’s too long introduces several serious hazards:
- Outside the approval. Husqvarna says its 445 II and 450 II meet the EN ISO 11681-1 chainsaw safety requirements when fitted with the guide bar and chain combinations listed in the manual.
- Kickback. Husqvarna says kickback happens when the kickback zone of the bar nose touches an object, and its manual sets limits on the bar nose radius.
- Maker liability. Makita says it accepts no responsibility for accidents or damage if non-approved bars or saw chains are used (UC3551A manual).
How to Fit a Longer Bar Safely
If your manual says you can safely go to 18 inches and your saw currently has a 14-inch bar, here’s the correct process:
- Check your manual for the maximum approved bar length.
- Buy a replacement bar listed for your saw, matching its pitch, gauge and bar mount.
- Buy a chain with the drive-link count listed for the new bar; Oregon says counts differ between bar makers, so don’t work it out from the old chain.
- Stop the engine and let it cool.
- Remove the clutch cover and loosen the bar mounting bolts.
- Slide off the old bar and chain.
- Fit the new bar and chain, ensuring the chain is centred on the bar.
- Tension the chain cool and with the engine off, following your manual. Oregon says that at the right tension the drive links stay fully seated in the bar groove and the tie straps lightly touch the bar.
- Check the oiler: the Ryobi and WORX manuals say to run the saw with the bar tip pointed at cardboard, paper or a light-coloured surface and look for a line of oil.
Frequently Asked Questions
Can I fit a 16-inch bar on a 12-inch chainsaw?
Only if your manual lists a 16-inch bar for that saw. Check the technical data first — if the longest bar listed is 14 inches, don’t exceed it.
Will a longer bar make my chainsaw cut faster?
We have no maker data comparing cutting speed by bar length. A longer bar lets you cut thicker wood in one pass.
What’s the most common bar upgrade?
We have no data on which upgrades are most common. Many manuals list several lengths for one saw — Stihl, for example, lists 30, 35 and 40 cm bars for the MS 170.
If I fit a longer bar, do I need a new spark plug?
We found no maker guidance that an approved longer bar needs a different spark plug or carburettor setting. Follow your manual.
Can I buy a bar and chain kit from a different brand?
Yes, if the bar suits your saw’s mount, matches its pitch and gauge, and is a length your manual lists. Oregon’s part finder lists Oregon chains by saw model, and Oregon bar codes include the mount (for example A041). We have no maker data on oil-flow differences between brands.
What happens if I accidentally fit a bar that’s too long?
Stop and refit a bar length your manual lists. Husqvarna says its 445 II and 450 II meet the EN ISO 11681-1 chainsaw safety requirements when fitted with the guide bar and chain combinations listed in the manual.
Is a longer bar worth the cost?
If your manual lists the longer bar and you regularly cut wood thicker than your current bar can handle, yes. A 14-to-16-inch upgrade costs £40–60 for bar and chain and lets you cut larger logs in one pass.
Ready to Upgrade Your Bar?
Start by checking your chainsaw manual for the maximum approved bar length. Once you know you’re within limits, browse replacement bars on Amazon.
For more on finding the right chain length and pitch, see our complete chainsaw chain compatibility guide.
How we compile this guide
We cross-reference compatibility details against manufacturer specifications where available, official tool manuals, and the physical standards that govern fitment (bore sizes, arbor diameters, voltage platforms, connector types). We prioritise primary sources over retailer listings, flag anything we can’t confirm, and re-verify the data on a regular cycle. Where we give a buying recommendation, we tell you the reasoning — not just the link. More on our method →
