Chainsaw Bar Length Guide: What Size Do You Need?
Bar length decides the diameter of wood a chainsaw can cut, but a longer bar is only useful if the engine can pull it. This guide covers the two-cut rule, recommended versus maximum bar length, and the displacement each length needs.
What bar length actually measures
The bar length printed on a spec sheet is the nominal length: a round number of inches picked by the manufacturer. It is not the length of chain that meets wood. Two to three centimetres of the bar sit inside the powerhead, clamped under the side cover and wrapped around the drive sprocket. What sticks out is the usable cutting length, and that is what decides the saw's real capacity.
This database normalises every bar figure to centimetres, so a saw sold as a 16-inch model is stored as bar_length_cm = 40.64. Subtract roughly 3 cm and you are left with about 38 cm of working steel. Every diameter figure below uses that convention.
The two-cut rule
A chainsaw does not stop working the moment a log is wider than its bar. It stops working comfortably.
- Single pass. If the diameter is at or below the usable length, the bar goes through in one movement. The powerhead stays on one side of the log, the kerf stays square, and both ends of the bar remain visible throughout. This is where a saw is fastest and most controllable.
- Two cuts. You cut from one side until the bar is past the centre of the log, then step around and cut in from the opposite side until you meet the first kerf. In theory that doubles your reach. In practice you need generous overlap to guarantee the two kerfs meet, and the second cut is half-blind. The realistic ceiling is about 1.7 times the usable length, not two.
The single-pass column below is the diameter you can cut cleanly and repeatedly; the two-cut column is an occasional maximum, not a daily working figure.
| Bar (nominal) | Usable length | Single-pass diameter | Two-cut maximum |
|---|---|---|---|
| 25.4 cm (10 in) | ~22 cm | up to 22 cm | ~37 cm |
| 30.5 cm (12 in) | ~27 cm | up to 27 cm | ~46 cm |
| 35.6 cm (14 in) | ~33 cm | up to 33 cm | ~55 cm |
| 40.6 cm (16 in) | ~38 cm | up to 38 cm | ~64 cm |
| 45.7 cm (18 in) | ~43 cm | up to 43 cm | ~72 cm |
| 50.8 cm (20 in) | ~48 cm | up to 48 cm | ~81 cm |
| 61.0 cm (24 in) | ~58 cm | up to 58 cm | ~98 cm |
Most firewood is under 40 cm across, which is exactly why 40 cm and 45 cm bars dominate the catalogue.
Bar length by task
| Bar | Typical work | Saws supplied at that length |
|---|---|---|
| 25-30 cm | Pruning, limbing, top-handle work off the ground | Stihl MS 151 (25.4 cm), Husqvarna T525 (30 cm), Stihl MS 201 (30.5 cm) |
| 35-36 cm | Property maintenance, storm cleanup, small firewood | Echo CS-310 (35.56 cm), Makita EA3200SRBB (35.56 cm) |
| 40-41 cm | The all-round homeowner size, and professional limbing | Husqvarna 435 (40 cm), Makita EA4300FRDB (40.64 cm), Stihl MS 261 (40.6 cm) |
| 45-46 cm | Firewood in volume, felling small and medium trees | Stihl MS 251 (45.7 cm), Echo CS-400 (45.72 cm), Makita EA6100PREG (45.72 cm) |
| 50-51 cm | Heavier felling and bucking | Stihl MS 271 (50.8 cm), Husqvarna 450S Rancher (50 cm), Makita EA5000PRGG (50.8 cm) |
| 60 cm and up | Large-timber felling, land clearing, milling | Husqvarna 460 Rancher (60 cm), Echo CS-680 (rated to 68.6 cm), Echo CS-7310P (rated to 81.28 cm) |
Recommended length is not maximum length
Two fields are stored whenever a manufacturer publishes both: bar_length_cm, the length the saw ships with or is recommended to run, and bar_length_max_cm, the longest bar the powerhead is rated to drive. The gap between them tells you a lot.
The Husqvarna 455 Rancher is recommended at 50 cm and rated to 61 cm: eleven centimetres of headroom from a 55.5 cc engine. The Husqvarna 435 ships at 40 cm and is rated to 45.72 cm.
At the other extreme, some saws have essentially no headroom. The Husqvarna T525 is recommended at 30 cm and rated to 30.48 cm, and the Milwaukee 2826-20T records 35.56 cm in both fields. On those machines the recommended length is the maximum, and there is no upgrade path.
The widest span in the database belongs to the Husqvarna 564XP Fuel Injected: recommended at 38.1 cm, rated to 71.1 cm. A 62.4 cc engine will physically turn a 71 cm bar, but it is specified at 38.1 cm because that is where it works at professional speed.
Displacement has to scale with the bar
The reason a longer bar is not simply better is that the engine has to pull more chain through more wood. Working the ratio out from the recorded specifications gives a remarkably consistent number.
| Model | Displacement | Recommended bar | cc per cm of bar |
|---|---|---|---|
| Stihl MS 151 | 22.93 cc | 25.4 cm | 0.90 |
| Husqvarna T525 | 27 cc | 30 cm | 0.90 |
| Echo CS-310 | 30.5 cc | 35.56 cm | 0.86 |
| Husqvarna 435 | 40.9 cc | 40 cm | 1.02 |
| Stihl MS 251 | 45.9 cc | 45.7 cm | 1.00 |
| Husqvarna 450S Rancher | 50.2 cc | 50 cm | 1.00 |
| Husqvarna 460 Rancher | 60.3 cc | 60 cm | 1.01 |
Across three brands and a near threefold range of engine sizes, manufacturers land between roughly 0.86 and 1.02 cc of displacement per centimetre of recommended bar. Call it one cc per centimetre and you have a usable sanity check for any petrol saw.
Run the same arithmetic against the maximum rated bar and the ratio drops by about ten per cent: the 455 Rancher works out at 0.91 cc/cm at 61 cm, the Echo CS-620P at 0.87 cc/cm at 68.58 cm, and the 564XP at 0.88 cc/cm at 71.1 cm. That is the reserve manufacturers build in: real, but narrow, and spent the moment you fit the longest bar on the list.
Over-barring, the most common mistake
Over-barring means fitting a bar near or beyond the powerhead's rating and then asking it to cut at that length all day. It is tempting: a longer bar looks like more capability for no extra money. What actually happens is this:
- Chain speed falls under load. The engine cannot hold its power band, the cutters stop clearing full chips, and the saw starts producing dust instead of shavings.
- The engine runs hot for longer. Two-stroke engines are cooled by airflow and by the fuel charge itself; sustained lugging is how they get damaged.
- Bar and chain wear accelerate. More chain in the cut means more heat at the bar rails and more oil demand than the pump was sized for.
- The saw becomes nose-heavy. A bar 15 cm longer than intended shifts the balance forward, and the operator feels it first.
The failure mode is not dramatic: a saw that cuts slowly, needs sharpening constantly, and wears out early. Compare a Stihl MS 182 at 36.1 cc on its 40.6 cm bar with a Stihl MS 261 at 50.8 cc on the same 40.6 cm bar: identical cutting length, 14.7 cc apart. The second saw is the one that finishes a full day of it.
Work backwards from the wood
Measure the largest wood you cut regularly, not the largest you have ever cut. Add three centimetres for the portion of bar inside the housing, round up to the next nominal size, and check that the saw's displacement is at least equal to that bar length expressed in centimetres. If the answer is a bar sitting close to the powerhead's maximum, move up an engine size instead of a bar size.
For the full decision, including power source, weight and duty class, start with the complete chainsaw buying guide, and use the comparison pages to put two candidates side by side.