Inquisitor is “54mm heroic” scale. So the average human mini is 54mm from the base of foot to the eye (also called 1/32 scale). And the minis are “heroic” as they are bulkier, especially the hands and head and weapons which are much larger in proportion to the rest of the mini. That said, 54mm inq models are a little better proportioned than 28mm GW minis.

A 40k catachan. Though 28mm, this shows the heroic proportions that Games workshop uses. Bigger heads, wrists/hands, weapons, and equipment, overall a more chunkier model. The red outline is a realistically proportioned figure [pic from the Alkony website].
On the left is a 28mm GW Eisenhorn from the Black Library celebration 2018 (Retails for AU$55. What the F#*k!). On the right, the 54mm Eisenhorn released with the inquisitor game. I’ve resized the pic so we can compare. The 54mm version has similar head and hand proportions as the 28mm version, so pretty much still heroic size. note: This is probably not the best example of heroic scale as the 28mm eisenhorn is slightly better proportioned than other gw tabletop minis.
On the left is a 28mm tabletop watch captain artemis ($AU40. oh what a steal of a deal!). On the right is the inquisitor 54mm scale version (again shrunk for comparison). The inq version has a slightly thinner head and smaller weapons, but surprisingly bulkier armour and backpack. Overall, very comparable.

But back to talking about scale. I guess i am somewhat of a purist when i prefer that ALL inquisitor minis should be at the right size. So what do i mean by this? I mean that the height of the each mini should be consistent with the fluff. So ratlings and squats are smaller than humans. Humans are smaller than eldar. Both are smaller than space marines. And ogryns tower over them all. Now i understand the opposing argument…if we take humans for example, in a sci-fi universe, there would be a huge diversity in heights. But i find it visually appealing and somehow ‘right’ if they are sized appropriately at a glance.

Now this may not always be possible, but i applaud those that make the effort to do so. And even in 28mm 40k, i appreciate the wave of 40k players who went about making their space marines ‘true scale’

A 28mm truescale space marine, modified at the legs to increase the height of the mini

When buying minis from other ranges, the scaling system is imperfect, and a lot of companies are very loose with the scale. They may advertise a mini as 54mm but it may be quite a bit bigger (or smaller) than 54mm from foot to eye. So some care is needed when buying a mini. Still there are many other scales that can be re-purposed for inq54.

54mm or 1/32: In theory, minis at this scale should fit inquisitor perfectly. But as inquisitor minis are heroic size, other minis may appear a bit slender when on a 40mm base. Or the heads and hands and weapons may seem a bit small. Sometimes the opposite happens and the minis from other ranges are quite a bit larger or bulkier. Andreas is probably the most well known brand using this scale, though there are many others too. This scale has the most figures as it has catered to the historic figures crowd for many years now.

1/35: I almost always find that these figures are too small and need some conversion. Bulkier 1/35 models tend to scale up OK to 54mm well when you kitbash them. Often the hands and head are still very small and the weapons are very thin, so they will need replacing. But once replaced, they tend to fit the heroic dimensions of inq54 a bit better. For non-bulky 1/35 scale minis, it can be very hard to make them look 54mm without major re-working.

1/24, but everyone calls it 75mm: Will be too big out of the box. It will often be the case that you will see a mini that is perfect for inquisitor, only to find that it is a 75mm scale mini. Blacksun miniatures, Scale75 and Nutsplanet use this scale a lot. Kickstarters commonly prefer this scale too. Lately it seems that kickstarters have two options (35mm or 75mm. But no love for 54mm!) If you choose your mini carefully, you may be able to chop these minis down a little, but it is still very hard to get them to 54mm height.

70mm: Some minis are in this scale. You can probably get away with minis in this scale being space marines (same with 75mm).

28mm or 32mm: eg Games Workshop tabletop. Oversized creatures in this scale such as ogryns are slightly small for inq54mm humans. They are more squat sized, unless you convert them by extending their height.

90mm, 120mm or larger: If you are making minis this big as a GM, you must really hate your players 🙂

It is usually much easier to increase the height of a mini than it is to decrease the height. So 1/35 scale minis can be extended at the waist of legs. Resizing larger minis can be somewhat difficult, but i generally cut them down at the just above the waist, or the upper legs and the calves or ankle. I generally don’t resize at the chest or shoulders as their is too much sculpted detail. Sometimes you may need to also reduce the length of the mini’s arms, but i think you can generally get away with not doing this. Here are some examples of some minis i have resized…