Problem with grid & width

[aksld]

Hello,

I work with WooCommerce on WordPress.
I replace the default gallery with Swiper.

The column that fits Swiper is float: left with a width set to 40%.

I created a simple slider:

const thumbs = new Swiper('.swiper-thumbs', {
  slidesPerView: 4,
  grid: {
    fill: 'row',
    rows: 2,
  },
});

Width of .swiper div: 524.8px
Width of swiper-slide div 131.25px

131.25 * 4 = 525px

In my display, I have 3 slides per line instead of 4.

However, if I set a fixed size, it works fine.

Is this a normal problem?
Is having a container calculated in % a problem?

Thanks in advance