How thick and heavy is futon ?

The weight of cotton filling

The following weight plus the weight of the fabric (up to 3.3 lb / 1.5kg,  depending on the size) is the actual weight.

Futon Mattress (Shiki Futon) 
Baby   6.6 lb / 3.0 kg
Single   13.2 lb / 6.0 kg
Single Long   15.4 lb / 7.0 kg
Super Long   16.7 lb / 7.6 kg
Semi Double   15.4 lb / 7.0 kg
Double   17.6 lb / 8.0 kg
Queen   19.8 lb / 9.0 kg

For adding extra cotton filling to your futon mattress, please visit this page

Futon Topper (30% Thinner Shiki Futon)
Single   8.8 lb / 4.0 kg
Single Long   10.5 lb / 4.8 kg
Super Long   11.0 lb / 5.1 kg
Semi Double   10.5 lb / 4.8 kg
Double   11.0 lb / 5.0 kg
Queen   13.2 kg / 6.0 kg

Futon Quilt (Kake Futon)
Baby   2.2 lb / 1.0 kg
Single   7.9 lb / 3.6 kg
Single Long   9.9 lb / 4.5 kg  
Semi Double   10.5 lb / 4.8 kg
Double   11.0 lb / 5.0 kg
Queen   12.1 lb / 5.5 kg

Kotatsu Futon 
Square   7.9 lb / 3.6 kg
Rectangle  9.9 lb / 4.5 kg

Zabuton (Cushion)
Meisen   2.6 lb / 1.2 kg
Hattan   3.1 lb / 1.4 kg
Meoto   4.4 lb / 2.0 kg  

All weights are approximate.