Band Saw Blade Length Calculator

How the math works

Picture the blade laid flat around two pulleys. Each straight run is about as long as the distance between axle centers, so the two runs together are 2 × C. Half of each wheel’s circumference is wrapped, so the curved parts add π × (D1 + D2) ÷ 2. When the wheels are different sizes the straight runs tilt slightly and get a little longer; the last term, (D1 − D2)² ÷ (4 × C), covers that.

L = 2C + π(D1 + D2)/2 + (D1 − D2)²/(4C)

With equal wheels the last term is zero and the formula collapses to 2C + πD. That is why a 14 in saw that takes the common 93½ in blade must have its axles about 24.76 in apart at working tension: (93.5 − π × 14) ÷ 2 = 24.76.

Reference lengths for equal wheels

Each row is the calculator run on the wheel size and center distance shown. Use it to sanity-check a measurement, not as a model list; two saws with the same wheel size can have quite different frames.

The 14 in / 30.75 in row is a 14 in saw with a 6 in riser block fitted to a 24.75 in base: adding a riser adds twice its height to the blade, so 93.48 + 12 = 105.48 in.

Worked examples

1. A used 14 in saw with no manual. Both wheels measure 14 in over the tires. With the tension knob backed off to mid-travel, the axles are 24.75 in apart. L = 49.50 + 43.98 + 0 = 93.48 in. A stock 93½ in blade will sit right in the middle of the tension range, which is what you want.

2. A shop-built saw with unequal wheels. Upper wheel 14 in, lower drive wheel 16 in, axles 30 in apart. Straight runs 60.00 in, wrap π × 30 ÷ 2 = 47.12 in, correction (16 − 14)² ÷ 120 = 0.033 in. Total 107.16 in. The correction is tiny here, but it grows quickly if the wheels differ a lot or sit close together.

3. Finding the blade band. Tick “Also compute a length range” and enter the upper wheel at the bottom (24 in) and top (25.5 in) of its travel. The calculator returns 91.98 in to 94.98 in. Any welded blade inside that band will tension; pick one near the middle so a slightly stretched blade or a new tire still has adjustment left.

Mistakes that cost a blade

• Measuring the wheel rim, not the tire. The blade rides on the tire, so measure across the tire crown. On a 14 in saw a worn tire versus a new one can move the answer by a quarter inch or more.
• Measuring axle spacing with the tension fully released. Set the upper wheel where it sits with a blade tensioned, or measure both ends of travel and use the range option.
• Trusting a nominal size. A “14 in” saw does not always have exactly 14 in wheels. Measure.
• Forgetting the riser block. A 6 in riser adds 12 in of blade, not 6.
• Mixing inches and millimetres. Pick one unit for all three measurements; the result is also shown in the other unit.

Shop tips

If the frame makes the axles hard to reach, wrap a length of non-stretch cord around both wheels with the upper wheel at mid-travel, mark the overlap, and measure the cord. It should agree with the calculator within about ¼ in; if it does not, recheck the wheel diameters.

Blade suppliers weld to order, so you are not limited to catalog lengths. When ordering, give the length to the nearest ¼ in along with width, TPI and thickness. Thinner blades (0.020–0.025 in) suit 14 in and smaller wheels; thick blades on small wheels fatigue and crack at the weld.

Safety

Unplug the saw before measuring inside the wheel covers. Coiled blades store a lot of energy: wear gloves and eye protection when uncoiling or folding a blade, and keep it pointed away from your face. Never run a blade that only just reaches tension — it can slip off the wheels under load.

Ordering the blade: the other four numbers

Length gets the blade onto the saw; the rest of the specification decides how it cuts. When you order a welded blade, give all five:

• Width sets the tightest curve. A widely published guide: ⅛ in blade, about ⅛ in radius; ¼ in, about ⅝ in; ⅜ in, about 1¼ in; ½ in, about 2½ in; ¾ in, about 5½ in. Use the widest blade that still makes the curve, because wider blades track straighter.
• Teeth per inch. Aim for at least three teeth in the work at all times. Thin stock wants fine teeth; thick resawing wants 2–4 TPI.
• Tooth form: regular for general and thin work, skip for softwood and plastics, hook for fast ripping and resawing.
• Thickness (gauge). Thinner blades flex around small wheels without cracking; 0.025 in is a common choice for 14 in saws.
• Material: carbon steel for most woodworking, bi-metal for metal and long life, carbide-tipped for heavy resawing.

Once the blade arrives, check it against the calculator before you fold the old one away: hang it over the wheels with the tension backed off. If the upper wheel needs more than about half its travel to tension it, the blade is on the long side of the band.

FAQ