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Coiled cable length calculator

Hey, fellow DIY custom cable builder! Here you can find two of my simple tools to help with coiled cable length calculation. Because doing the math can be confusing if you have a coiled part.

Now you can calculate (1) the full cable lenght needed to get an expected width of coil. Alternatively, you can (2) calculate the greatest possible coil width at a given lenght of cable.

First some basic measures

Cable thickness: cm
Coil/wrap inner diameter, rod/stick outer diameter: cm

Base of the calculation: you need about 4.4 cm of bare USB cable (thickness: 0.4 cm) for one wrap - wrapped around a 1 cm thick rod/bar.

1. Calculate the lenght of cable/sleeve needed

A Straight lenght on the device/keyboard end: cm
B Width of the coiled part: cm
C Straight lenght on the PC side: cm
Full length of cable needed: cm

2. Max width of coiled part at a given cable lenght

A Full cable length available: cm
B Straight length on the device/keyboard end: cm
C Straight length on the PC side: cm
Width of the coiled part: cm

USB operating specifications limit the maximum length of the cable to 5 meters (16 feet) for full speed devices and 3 meters (10 feet) for any low speed devices. Anything longer than that, and the cable risks to fail transmitting properly.

With keyboards drawing more power (eg. lots of LEDs), a maximum length of 3 m or less is preferable.

Based on zapcable's testing there are some high-powered keyboards that require even shorter cables—like HHKB keyboards (2.4 m / 8 feet) and Input Club’s K-Type or Massdrop’s CTRL (2.1 m / 7 feet).