Its radius is calculated to be around 668 solar radii[6] (4.65 × 108 km, 3.10 au).

This corresponds to a volume 298 million times bigger than the Sun.

If placed at the center of the Solar System, Westerlund 1-75 would engulf the inner limits of the asteroid belt.

The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.

Using the effective temperature of 3,600 K,[6] the bolometric luminosity of 68,000 L☉[6] and the solar effective temperature of 5,772 K,[8] the radius of Westerlund 1-75 can be calculated using the Stefan-Boltzmann law at 668 R☉.