im new to GMing so im not to sure how many bad guys to throw at my players at the start.

to much and ill kill them all and to little its to easy for them.

What I've done in one of the first battles with my first group was splitting up the enemy in different groups. The players were infiltrating a clandestine little space port. In the hangar they found a first crew of gangers working on a guncutter and my players opened fire. This caused an alarm to go off and warned other gangers.

I had set certain amounts of time for every other group of gangers at the complex (the garage, the tower, the auspexarray), but you could easily wing it and make a new group of gangers burst out of the door when your players (almost) killed all of the gangers of the first group.

My players, more accustomed to fixed combat (one encounter) were surprised when a second group came through the door. They panicked a bit when a third group came in and they had to start reloading their guns, thus leaving room for the thugs to close the distance. They were really exasperated when the fourth and final group ran in, led by the ringleader with a savage chainsword. I almost screwed up since of the players went down after he catched a bad case of chainsword to the head, resulting in loss of sight and consciousness. Thanks the Emperor for faith points;

Although the gangers were nothing much to look at individually, even in group, they were a nice challenge as a whole. And the beauty of it is that you as a GM can stop the tap of gangers at any point during the encounter.

Dark Heresy has a lethal system.

And the players should be aware that during a surprise round they can all be killed, equally they can kill them enemy in a surprise round.

There is no encounter level (ECL), so the best way is start them off with some easy, but smart opponents and then when you know how badly they got hurt you can then up the lethality. You may end up killing characters, but that is part of the game.

I also recommend with combat rolling in the open, the less fudging you do, the more fun everyone has. I've had players talk about how awesomely lucky an opponent was with a grenade when it killed the warband.

You also have access to their stats / Skills & Talents - try and run a few fake battles by yourself to gauge the difficulty - using only Standard Attacks for the enemies.

Then factor in special attacks like Charge, All-Out, Full-Auto Bursts, range, cover, lighting modifiers, etc. on both sides.

The difficulty of taking down 3 scraggly mutants greatly increases if a group of say, six Acolytes are caught by surprise, are fighting in the dark, on a crumbling underhive bridge, during a hivequake, etc etc.

There's really no science to encounter design in 40k RPG. You really just have to feel it out. It's not the best system in terms of encounter design. Err on the side of 'too easy' and, as Astelan did, add more groups of guys if the encounter is going to easily.

As Keffish said, you might want to check some easy numbers:

• If i give the enemies x armour and x thoughnessbonus, how much damage do the acolytes have to do to scratch them. Take penetration into account if your acolytes have access to weapons with penetration.
• Furthermore, you can take into account the number of wounds your enemies possess off. if you put the above together with this, you can find out how hard it will be to kill off your opponents.
• Check how easy it is for the opponents to hit (WS & BS) and how much damage they can inflict. Compare this to the armour and thoughness of the players.

Finally, you should check whether your opponents will actually be in position to do damage. If you put 4 swordsmen at 200 meters away, chances are that your acolytes will have fried them before they even get into a position to do damage.

It's really dependent on group composition. Four lore monkeys won't be able to handle the same thing as four combat monkeys.

It's really dependent on group composition. Four lore monkeys won't be able to handle the same thing as four combat monkeys.

Luckily, Lore monkeys can suppressive fire and run away as well as anyone else and throw grenades!

Dark Heresy 2 gives NPCs challenge ratings which you tally up with your groups average XP. It ought to provide a relatively fair fight.

As has been said however, it's a very lethal system and it's very easy to underestimate how much damage the PCs and NPCs will chuck out in a turn. Another important bit: The players are the stars of the show, there's nothing wrong with letting them show off a bit in some early on combats. They shouldn't be fighting anything too lethal. If it's some bar fight they instigate by asking the wrong question then there'd be no need for gangers to draw guns and knives, it's just a bar brawl to scare off some jumped-up off-worlders after all!

Dark Heresy 2 gives NPCs challenge ratings which you tally up with your groups average XP. It ought to provide a relatively fair fight.

It's fairly hit or miss (pun intended). It comes down to how smart you play the enemy as well.

I found that three or four, for a party of four, up-armoured servitors were quite fun for my group as they presented a threat that if allowed to get up close and personal could cause a bit of damage, along with a single 'ring-leader' human with a gun. This made them think about the entire environment as well as target priority. Although, I know that not all parties will react this way, so it would be in the first few combats to address the combat system and any weaknesses of the group.

The second engagement I almost ended up one hitting a character because he was so used to standing and shooting while the hoard bore down on him. Now he is much more careful to avoid the muzzle of a stubber.