Spocalc 2022 is the updated full-strength version and includes hub and rim databases. [No longer being updated, but we link to others which are being updated]

Spocalc is the full-strength version and includes hub and rim databases. [No longer being updated, but we link to others which are being updated]

SpocalcExpress has no hub database, no rim database, no instructions, no macros -- just the calculations that operate on the numbers you enter.

Thank Mark Schlueter for this great idea. SpocalcExpress is just like the full version of Spocalc, but less.
Enter one set of hub and rim dimensions and SpocalcExpress gives you the spoke length for radial, 1, 2, 3, 4, and any other cross of your choice. Great for Quicksheet on your Palm.

Spocalc is a free Excel spreadsheet I made that calculates spoke lengths for wire-spoked wheels. There are lots of other spoke calculators on the web (see the list I've assembled). Some require you to measure your own rim and hub, but Spocalc includes a database of over 350 hubs and 500 rims. The Spocalc database is also user-modifiable and expandable so you can add more rims and hubs.

Some other spoke calculators require you to re-enter the rim and hub dimensions again and again to get different lengths for different numbers of crosses, but Spocalc automatically gives you spoke lengths for 0, 1, 2, 3, 4 and one other cross of your choosing (even a decimal number! Why would you want to do that?). Having several lengths can come in handy. Print out Spocalc's calculator sheet and take it with you when you buy spokes. If the shop doesn't have the right length for, say, three cross, you can take a glance at the sheet and decide if you could use four cross instead.

Matt Armstrong has updated Spocalc 2022, with ease-of use features. You must have Microsoft Excel 2007 or higher to run this version.. For other versions on this site, you must have Microsoft Excel 97 or higher (Windows, Mac or Android), LibreOffice Calc (free download, Windows or Linux, also see page about format conversion), or Gnumeric (free download, Linux only).

Spocalc has a few macros to help speed data entry. Spocalc 2022 makes them easy to access, with buttons.

Opening the macros is a bit harder with earlier versions: you must choose "Enable.". If your virus checker disables them you can still use Spocalc without the macros - you just have to type in the numbers by hand.

In Excel 5.0, macros run from the Tools menu. In newer Excel versions which have ribbons instead of menus, there is no Tools menu, and also no Help menu. Clicking on the tiny question mark at the right-hand side of the ribbon and searching on "Using macros" led me to information:

1. If the Developer tab is not in the ribbon, then in the File tab, click Options, and then the Customize Ribbon category.
2. In the Main Tabs list, select the Developer check box, and "OK."
3. Then, in the Developer tab of the ribbon, click on "Macro Security."
4. In Macro Security, click on "Disable all macros with notification."

This choice will let you decide whether to run macros or not. A message bar may still come up, warning that macros are disabled. If so, click to enable macros.

Now to use a macro, first select a hub or rim by name, as described below. Then in the Developer tab, click on the Macros icon.: A list of macros will appear. Click on the appropriate macro.

macros run under Microsoft Excel (Windows, Mac) but...

Versions of spocalc with macros for OpenOffice have been prepared by Mike Sherman.

As you can see, by entering the hub and rim dimensions once, you get spoke lengths for all crosses automatically.

Although front wheels are usually symmetrical, which would make the "Left Front" and "Right Front" tables redundant, I've provided separate left and right tables in case you are using a disc-brake hub or other dished front hub.

At the bottom you can see the tabs used to view the instructions and the hub and rim database sheets.

While you may certainly type in the numbers by hand, here you can see how to use the macros to enter all the hub data for you.

Important macro tip: you must first select a cell in the "Select a Hub" column before using the macro to enter the data.

The rims sheet works just like the hubs sheet: select the cell containing the rim you are using, then click on the appropriate Macro (from the Tools menu, or in the Developer Tab of newer, beribboned Excel versions) to enter the Effective Rim Diameter (ERD) on the calculator page, or type the ERD number into the calculator page by hand.

The Exact Way: The idea is to adjust the hub widths to mimic the rim offset. (The change in spoke length is the same whether the rim moves relative to the hub, or the hub moves relative to the rim.) To do this, just change the left and right flange offsets by the rim offset. Here's how to do it, step by step:

After entering your hub data into Spocalc,

1. Calculate your rim's spoke-hole lateral offset:
- Measure the rim width (W) and divide by two. This is the rim half-width.
- Measure the distance from the near sidewall to the center of the average spoke hole (L).
- Subtract this number from the rim half-width.

The result is the rim's spoke hole lateral offset (or just rim offset), i.e. the amount by which the rim reduces your wheel's dish. It is usually a couple of millimeters. Thus,

2. Type over the "W, width from center to flange" hub dimensions in Spocalc:
- Add the rim offset to the right flange width, and
- Subtract rim offset from the left flange width.

Spocalc automatically displays the new spoke lengths.

Fatbike rims typically have the two rows of spoke holes far from the centerline. With some hubs, there will be hardly any bracing angle unless you cross spokes over to the far side of the rim. An e-bike hub motor may have narrow spacing between the flanges, so crossing the spokes over may also be useful. Use a rim whose spoke holes are not angled sharply toward the flange on their side. Add the offset between the centerline and the far row of spoke holes to the hub flange spacing when calculating spoke length -- same calculation as the "hard way" for asymmetric rims, described above, except that you have to do it separately for each side of the rim. .

The spoke lengths calculated in Spocalc are based on pure 3D trigonometry: they are exact. So unless I've made a mistake in the formulas, any error must lie in the hub or rim measurements.

1. Check and double check "ERD, effective rim diameter". Errors in ERD have a direct effect on spoke length. ERD is also the easiest to get wrong, since rims are rarely round when not built into wheels, and you may measure at a large or small diameter. It is definitely worth measuring ERD at several locations around the rim and averaging. The idea is to reduce the effect of any single measurement falling at a high or low spot. [I describe two additional ways to measure rim diameter in my article on this site -- John Allen]

2. Hub dimensions are less critical: errors here have less effect on spoke length than errors in ERD. With tangential lacing (several crosses, like three or four), flange diameter (d) is less critical than flange width (W). With radial lacing (not advisable with hub brakes or rear wheels) flange diameter becomes relatively more important.

3. Spoke-hole diameter (S) is pretty inconsequential. Errors in spoke-hole diameter contribute directly to errors in spoke length, but since the errors are usually so small (much less than 1 mm) they rarely make a significant difference in spoke length. Many formulas ignore spoke-hole diameter entirely.

4. Also, it may seem obvious, but check to be sure you entered the correct number of spokes (N), and that you read the spoke length from the cell corresponding to the correct number of crosses. I've made both those mistakes before!

5. You can always download a current copy of Spocalc or SpocalcExpress from this page. This will fix problems like accidentally typing over hub or rim dimensions on the database sheets, or typing over formulas on the calculator sheet.

"Hey Damon, I got the macros working. In the Excel [2000] program. Go under Tools, Macros, then Security. Three options are there. I set mine on medium security. Just thought I'd let you know in case others have the same problem. Thanks for the help and the great spoke calculator." -Bob