This spoke length calculator can be used to figure out which lacing
pattern to use, and how long the spokes will need to be. It supports many
unusual features, such as mixed lacing, offset frames and rims, and high-low
hubs. To help decide which lacing pattern to use, it computes spoke pull
angles. It also computes spoke tensions for dished wheels and uses this
to compute spoke stretch for a little extra accuracy.
All measurements are in mm. Use a decent vernier caliper for accuracy.
If you're building both front and rear wheels, measure both rims and hubs.
As front wheels are always symmetric, you'll enter the same data for both
drive and non-drive sides.
Enter the wheel data:
Measure your rim:
- Enter the number of spokes. This is typically 32 or 36, with 32 being
more common today. I recommend verifying that your rim and hub are compatible.
Jobst Brandt*, among
others, recommends using more thin spokes rather than fewer thick spokes
- Enter the lacing pattern. A good rule of thumb
is to divide the number of spokes by 9, rounding down. This gives 3-cross
for 32h wheels and 4-cross for 36h wheels. Most wheels are built 3-cross
today. You can experiment to see what pattern gives you the most tangential
spoke pull angle. Using too many crosses can cause spoke head interference
problems at the hub for very large or small hub flanges. It can also cause
the spokes to enter the rim at too great a angle for very small rims. For
example, it's probably best to avoid 4-cross on a 36 spoke BMX wheel. Normally,
both sides will use the same lacing. Use 0 for radial lacing (not recommended).
- Enter the offset. This should be zero except for frames with their
dropouts off-center. Use a positive number if the dropouts are shifted
towards the drive side (to reduce wheel dish).
Measure your hub:
- If your rim is listed in the rim menu, you can choose it to load the
data for that rim. If not, proceed with your measurements...
- Measure several diameters and average them. Use spoke nipples and old
spokes, as described in Roger Musson's**
for his spoke length calculator.
However, for this calculator, measure from the top of the nipple since
spoke stretch is calculated precisely. Note that this is the most important
measurement, so do this carefully!
- Measure the hole offsets relative to the center of the rim, measured
perpendicular to the rim. Normally, the drive and non-drive offsets will
be equal and positive. For offset rims such as the Ritchey Rock OCX, the
drive hole offset may be negative, indicating that it's to the left
of the center of the rim. For example, offsets of -5.0 mm (drive) and 7.0
mm (non-drive) would indicate that the holes are staggered by 2.0 mm and
are offset towards the non-drive side by 6.0 mm. This would produce approximately
the same spoke tension on the drive and non-drive sides for a typical rear
Enter the spoke data:
- If your hub is listed in the hub menu, you can choose it to load the
data for that hub. If not, proceed with your measurements...
- Measure the axle length between the flat spots which seat against the
dropouts. The axle will extend several millimeters beyond this on either
- Measure the flange insets by placing the hub over a hole so that the
axle sticks down into the hole. Then measure vertically from the outer
edge of the flange down to the surface. For rear hubs, repeat for the other
- Measure the flange diameter by averaging measurements from the inner
and outer edges of the holes. Then divide by 2 to get the radius. For high-low
hubs, measure both ends.
- Measure the hole diameter by finding a nail or similar object which
just barely fits. This is also a fairly sensitive measurement.
Press the Calculate button:
- If your spokes are listed in the spoke menus, you can choose them to
load the data for those spokes. If not, proceed with your measurements...
- For straight gauge spokes, enter the spoke diameter under both "diameter"
and "butt diameter". Use 2.0 for 14g or 1.8 for 15g. Enter a
butt length of 0.
- For butted spokes, enter the larger diameter under "diameter"
and the narrower diameter under "butt diameter". Use 1.8 for
15g or 1.6 for 16g. For other gauges, measure the spoke diameter. Measure
the length of the narrow section and enter it under "butt length".
Use your finger tips to see where the spoke changes diameter if you can't
- If "Invalid data" shows up in the status bar, the field with
invalid data gets focus. Either there is a typo, or the value is out of
- Experiment with different lacing patterns to see which gives the most
tangential (closest to 90 degrees) spoke pull angles, as described above.
- When you are satisfied with everything, take the lengths shown and
round down to the nearest available length. Many stores only stock even
lengths, but odd lengths are available. For very short spokes, you may
have to have a store cut spokes for you, but my advice is to order pre-cut
spokes if you can find them.
Make initial values be blank instead of zero.
Sort menus either alphabetically or in the order they appear in the
Possibly combine all the data into a single file for download efficiency.
Use Jdoc format for comments and put resulting html online.
Calculate angle spoke enters rim at. Roger
Musson suggested keeping this angle no more than 9 degrees from perpendicular.
If you find this useful or have any comments, please send me an email.
If you send me your measurements, I'll add them to the menus so the next
wheel builder won't have to repeat the process. If you find any of the
component data inaccurate, please let me know. I suspect there is quite
a bit of variation.
The maximum spoke tension (ie. that used on the drive side of a dished
wheel) is 180 N.
The desired spoke tension (ie. that used on undished wheels) is 3/4
of the maximum: 135 N.
Spokes are made of steel: modulus of elasticity = 21000 N/mm2
(from The Bicycle Wheel*).
Titanium spokes aren't recommended.
The calculator does not compensate for rim shrinkage due to spoke tension.
This can reduce the rim diameter by as much as 2 mm, depending on the rim.
* The Bicycle Wheel, by Jobst
Brandt. Formulae for approximating spoke stretch were taken from this
** Roger Musson's
spoke length calculator.
Ideas for measuring rims were taken from this web page.
This caculator was implemented on Mac OS X using Apple's Project Builder. Here's the source code.
This calculator uses JavaTM utilities
courtesy of Core
Java, by Gary Cornell and
Cay S. Horstmann.
article on wheelbuilding
includes lots of good detailed information while still being readable. It is highly
recommended. It includes links to several other spoke length calculators, several of
which include large databases of pre-measured components.
Version 10. August 3, 2003. Email Danny