A chainsaw that runs well depends on a bar and chain that match each other and fit the saw. Over time, chains stretch, cutting teeth dull beyond sharpening, and guide bars wear down or get bent. Replacing these parts is straightforward, but ordering the correct size requires knowing three measurements: bar length, chain pitch, and chain gauge. Order the wrong combination and the chain either will not fit or will not stay tensioned. Knowing how to measure a chainsaw bar and chain removes the guesswork and keeps the saw working safely. For those evaluating what saw to buy in the first place, selecting a small chainsaw based on power source, bar length, and essential features for property maintenance provides a solid starting point.
Before taking any measurements, safety comes first. Disconnect the chainsaw from its power source. For battery-powered models, remove the lithium-ion battery pack. For corded electric saws, unplug the tool from the outlet. For gas-powered saws, disconnect the spark plug wire. The chain teeth are sharp enough to cut skin on contact, so wearing protective gloves during measurement is recommended. Work on a stable surface with good lighting so you can read stamped numbers clearly.
Tools Needed and Safety Preparation
Measuring a chainsaw bar and chain requires minimal equipment. Gather a tape measure with both inches and millimeters, a scrench (the combination tool that comes with most chainsaws), coins of different denominations (quarter, dime, and penny), and a short length of string if you plan to measure chain pitch by an alternative method. Protective gloves complete the kit.
Preparing the Saw for Measurement
Lay the chainsaw on a flat surface with the bar side facing up. Remove the bar nuts that hold the side cover in place, then lift off the cover. Slide the bar and chain assembly off the studs and set it on the workbench. Clean any sawdust and oil residue from the bar before measuring, as debris can throw off readings by a fraction of an inch. For precision layout tips that apply to measurement tasks in general, the tape measure method for equal spacing and perfect layouts covers techniques useful in workshop and construction settings alike.
Reading Existing Stamped Numbers
Before reaching for the tape measure, inspect the bar for stamped numbers near the mounting end. Many bars have the length, pitch, and gauge stamped directly into the steel. On chains, the numbers are usually stamped into the drive links. A typical stamp reads something like 3/8 1.5 72, indicating 3/8 inch pitch, 0.050 inch gauge, and 72 drive links. Write these numbers down as a baseline before verifying with physical measurement.
Measuring the Chainsaw Bar Length Correctly
Bar length is the most commonly referenced measurement but also the most frequently misunderstood. What manufacturers call the bar length is not the full metal length of the bar from tip to mount. It is the effective cutting length, which is the distance from the front of the saw housing to the farthest point of the bar tip measured along the bar centerline.
Two Measurement Methods
The first method requires the bar mounted on the saw. Measure from where the bar emerges from the saw body to the tip of the bar. Round the measurement to the nearest whole inch. A bar that measures 18 inches from housing to tip is sold as an 18-inch bar, even though the actual metal length may be closer to 20 inches. For a more precise understanding of how measurement tools are used across different trades, tape measure uses including angle measurement and advanced techniques covers applications that extend beyond simple linear distance.
The second method requires removing the bar from the saw. Lay the bar flat and measure from the tip to the center of the bar mount slot or the center of the mounting stud holes. This gives the overall bar length, which will be longer than the advertised cutting length. For ordering purposes, use the cutting length measurement, not the overall length. Most retailers list bars by cutting length, so a 16-inch bar from a parts catalog matches a bar that cuts a 16-inch path through wood.
| Bar Cutting Length | Typical Saw Type | Common Applications | Chain Pitch Range |
|---|---|---|---|
| 12 to 14 inches | Electric and small battery | Pruning, limbing, small firewood | 1/4 or 3/8 low-profile |
| 16 to 18 inches | Mid-range gas and battery | General firewood, fence posts | 3/8 or .325 |
| 20 to 24 inches | Full-size gas | Felling, large firewood, bucking | 3/8 or .404 |
| 28 to 36 inches | Professional gas | Large tree felling, milling | .404 or 3/8 |
Determining Chain Pitch, Gauge, and Drive Link Count
Chain pitch and gauge are the two specifications that determine whether a chain fits a bar and a saw. Pitch is the distance between three consecutive rivets divided by two, measured from the center of one rivet to the center of the next. Gauge is the thickness of the drive link that rides in the bar groove. Both must match between chain and bar for the system to work.
How to Measure Chain Pitch
To measure pitch, place the tape measure or a ruler across three consecutive rivets on the chain. Measure from the center of the first rivet to the center of the third rivet, then divide by two. Standard pitch sizes are 1/4 inch (0.325 inch), 3/8 inch, and .404 inch. The 3/8 inch low-profile pitch is common on smaller homeowner saws and should not be confused with the standard 3/8 inch pitch used on larger equipment. Applying the same careful measurement principles used in other technical fields, the techniques described in how to measure discharge using a mouthpiece demonstrate how accurate measurement methods transfer across different disciplines.
How to Measure Chain Gauge
Gauge is measured with a caliper or by using the coin method with a coin of known thickness. The drive link tail is the flat section that rides in the bar groove. Place the caliper across the drive link tail to get the thickness in thousandths of an inch. Common gauges are 0.043 inch (low-profile), 0.050 inch (standard), 0.058 inch (heavy-duty), and 0.063 inch (full-house). A chain with the wrong gauge will either sit too loose in the bar groove or bind completely. Measuring thickness at the link tail with the same approach used for measuring soil suction in geotechnical applications highlights the importance of using calibrated tools for dimensional accuracy rather than relying on visual estimates.
Counting Drive Links and Verifying Compatibility
The drive link count determines the chain loop length. Even when pitch and gauge match, a chain with too many or too few drive links will not fit the bar. The count includes every drive link the chain has, not just the ones visible when the chain is mounted. For a chain already on the saw, turn the bar and chain assembly over, find the number stamped into the drive links, and confirm visually.
Drive Link Counting Method
Start at any drive link and count sequentially around the entire loop. Mark the starting link with a piece of tape or a marker so you do not lose your place. Most chains have between 40 and 84 drive links depending on bar length and pitch. A 16-inch bar with 3/8 inch low-profile pitch typically uses 55 to 60 drive links. A 20-inch bar with standard 3/8 inch pitch uses 72 drive links. When ordering a replacement, the exact count matters more than any other number. Always verify drive link count before placing an order. The systematic counting method parallels disciplined approaches found in measuring discharge using an orifice, where the precision of each measurement step directly affects the final result.
| Bar Length | Chain Pitch | Gauge | Typical Drive Links |
|---|---|---|---|
| 14 inch | 3/8 low-profile | 0.043 or 0.050 | 50 to 52 |
| 16 inch | 3/8 low-profile | 0.043 or 0.050 | 55 to 57 |
| 18 inch | .325 or 3/8 | 0.050 | 62 to 68 |
| 20 inch | .325 or 3/8 | 0.050 or 0.058 | 72 to 76 |
| 24 inch | .325 or 3/8 | 0.058 or 0.063 | 78 to 84 |
Using the Coin Method and Manufacturer Resources
When stamped numbers are worn off and calipers are not available, the coin method provides a practical way to identify chain pitch and gauge. A dime is approximately 0.053 inch thick, a penny is about 0.060 inch thick, and a quarter is roughly 0.069 inch thick. Fit the coin edge into the bar groove to test whether the groove width matches.
If the dime fits tightly, the gauge is likely 0.050 inch (the most common gauge for homeowner and pro-sumer saws). If the penny fits, the gauge is around 0.058 inch. If only the quarter fits, the gauge is 0.063 inch, typically found on large professional saws. For pitch estimation, place a coin between two drive links and measure the gap. This method is not precise enough for final ordering but confirms whether stamped numbers are in the right ballpark. When the bar or chain is too worn to read, the saw model number printed on the saw housing is the most reliable fallback. Enter the model number into the manufacturer parts lookup or search online for the OEM chain specifications. Cross-reference with the specifications printed in the owners manual if you still have it.
Replacing a chainsaw bar and chain does not require advanced skills, but it does demand accurate measurements. Bar length, chain pitch, chain gauge, and drive link count must all match. Spending five minutes measuring these four values prevents the frustration of ordering the wrong part and keeps the saw cutting safely. For a broader look at how this tool fits into construction and property work, the chainsaw in modern construction from timber framing to job site versatility covers applications that go well beyond firewood cutting.