I have a player who likes to use the shatter spell. The description says it will do the same damage to the targets' armor and weapons that it does to the targets. Right now, I don't have an easy chart that gives me an idea of how many hit points a suit of armor or sword has though. Any suggestions?
It only damages unattended items. Not worn gear.
From the Shatter spell description text in the 5e PHB:
A non-magical object that isn't being worn or carried also takes the damage if it's in the spell area.
5th Edition doesn't have formal item HP rules, but I'd make a ruling that the item gets a save and breaks if it is failed.
Item save modifier would be based on my estimation of its fragility.
As stated elsewhere; worn objects can't be targeted. An unattended suit of full plate mail would have 18(4d8) hp and an AC of 19.
Since this was posted back in September of 2014, 5e has released rules on how to interact with objects. While this would not change the correct answer above; you still can not damage attended or worn objects, we can add in some detail now about PC / object interaction.
Under the heading of Objects in the SRD. You can see that the appropriate object hit points for a medium sized resilient object is 18 or roll 4d8.
Object Hit Points
Medium (barrel, chandelier)......4(1d8)......18(4d8)
As a DM you might also consider adding a Damage Threshold to a suit of armor, although that would not matter much against a shatter spell.
An object with a damage threshold has immunity to all damage unless it takes an amount of damage from a single Attack or effect equal to or greater than its damage threshold, in which case it takes damage as normal. Any damage that fails to meet or exceed the object’s damage threshold is considered superficial and doesn’t reduce the object’s hit points.
The DM determines an object's Armor Class and hit points, and might decide that certain objects have resistance or immunity to certain kinds of attacks. (PHB 185)
Also as Carl T points out, this only applies to objects that are not being worn. The important thing here is that without this text, objects are immune to effects that require Con saves. So this simply allows damage to specific non-magical, non-worn items.
As a DM you should set the HP of the object, when it goes to 0, it's destroyed. There will likely be much more guidance on setting the HP (And AC) of objects in the DMG which will see release in December.