This set of miniatures comes pre-supported with custom base. There are 3 sizes (Standard Scale 32mm, Champion Scale 40mm and Collectible 75mm). You can find dimensions below. 

Product Details:
Standard 32mm scale with approx. 25mm base (height: 54.63mm, width: 35.82mm, length: 30.62mm)
Champion 40mm scale with approx. 30mm base (height: 62.28mm, width: 44.77mm, length: 38.28mm)
Collectible 75mm scale with approx. 50mm base (height: 128.03mm, width: 83.95mm, length: 71.77mm)

A little more information about Scale/Size:
Sometimes things can get a little confusing when trying to determine the scale of tabletop miniatures and collectibles, but I have boiled it down to 3 widely accepted scales.

Standard Scale 32mm: Measuring from the foot to the eyeline of a 6 foot humanoid standing upright should be 32mm or approximately 34-36mm to the top of the head. Everything in this scale is relevant to that measurement so creatures that are shorter or taller than a 6ft tall humanoid will scale accordingly (Reiner is a Goliath so he is significantly larger than a standard human). This is the scale that most tabletop companies use and for a standard humanoid (aka medium size) will fit within a 1 inch (25mm) square for tabletop mats. The benefit to this scale is that it will most likely fit most miniatures purchased at a retail store. The drawback to it is that sometimes proportions will have to be chonkier in order to see them at a distance and you have less surface area to apply paint.

Champion Scale 40mm: Measuring from the foot to the eyeline of a 6 foot humanoid standing upright should be 40mm or approximately 46-48mm to the top of the head. Everything in this scale is relevant to that measurement so creatures that are shorter or taller than a 6ft tall humanoid will scale accordingly. This is the scale that many wargame miniature companies have their hero or champion models sized at. Additionally, many STL miniature creators use in order to allow details to register on older resin 3d printers and is the scale I prefer for my own tabletop games. I do my best to make sure that a standard humanoid (aka medium size) will fit within a 1 inch (25mm) square for tabletop mats but sometimes a model at this scale will need a larger base for stability or depending on the pose. The benefit to this scale is that it allows for more detail to be present on the model, more surface area to apply paint techniques and will stand out on the tabletop (which is ideal for player characters or the BBEG). The drawback is that it may look out of scale compared to 32mm minis.

Collectible Scale 75mm: Measuring from the foot to the eyeline of a 6 foot humanoid standing upright should be 75mm or approximately 80mm to the top of the head. Everything in this scale is relevant to that measurement so creatures that are shorter or taller than a 6ft tall humanoid will scale accordingly. This is the scale that is widely used for collectible or professional showcase miniatures.