Checking my math on magic items

[TheElfLord]

I'm looking at buying a custom magic item for a game and wanted to be sure I had done my math correctly for the magic item guidelines.

My intention is to gain a pair of boots of expedious retreat. If I wanted to get a pair of command word activated boots that worked 3/times a day the math would be as follows:

(Spell level x caster level x 1800) [for the base price] / 1.66 [for the charges per day]

If i wanted it to last 2 mins at a time, I need a second level caster, so it would work out to be:

(1 x 2 x 1800) / 1.66 = 2169 gp

If on the other hand, I wanted continous expedious retreat boots, the math is:

spell level x caster level x 2000 x 2 [duration in mins modifier] or

1 x 1 x 2000 x 2 = 4000 gp


So is my math right?

[marjan]

For command word activated it is OK. For continuous you should check with your DM since those are only guidelines.
IMO 4k is cheap. Boots of Striding and Springing cost 5.5k and gives 10ft of speed and +5 to jump. +5 to jump = 2.5 which means that the rest is worth 3k, meaning that (price for 10ft) x 1.5 = 3k or 2k for +10ft. Given that prices for bonuses are exponential +30ft should be closer to 18k - 3^(3 times 10ft) x 2k.

[CASTLEMIKE]

Sounds like you are both right although I favor Marjan because of the duration of the base spells.

Two level 1 spells: Expeditious Retreat is +30 movement for 1/minute a level and Longstrider is +10 movement for 1/hour a level.

A good compromise might be Lesser Boots of Striding (Without Springing) for 3,000 gp which provide a continuous +10 land movement but it's your DM's call.

[TheElfLord]

Well I'm the DM, so thats not a major problem as I'm aware that the decision is mine. I was just making sure I read things properly.

[daggaz]

For Boots of continuous expiditios retreat, definitely compare it to other items of movement (as well as feats and classes etc..) to see how it pans out. Movement bonuses, especially large movement bonuses, are a powerful tool for a PC and should be costly if they are continuous.

You could triple the price of lesser boots of striding, but that would be too low still, as DnD prices usually rice exponentially rather than linearly (look at magic weapon bonus price progressions instead). In that case, you should probably multiply the cost of the boots by nine, rather than three.

That gives a cost of 27,000 gp, which seems fair to me at least for a continual effect of a normally short duration spell which gives a substantial boost to maneuvarability in combat. Especially since the boost is a good three times better than the class ability gained from taking a level in barbarian, for example.

The big lesson here is, always be very careful when dealing with continual effect items (or unlimited command activated items). Think to yourself, does this remind me of the ring of continual true strike? If its even remotely similiar, it needs to be hit with the expensive bat, or the nerf bat. Your pick.

[enderrocksonall]

according to the chart on page 285 of the DMG, the formula should be this:

Caster level x Spell level x 2000 X 1.5= base price.

With that formula you are looking at about 84,000 gp for a use activated or a continuous item of Freedom of Movement.

7th level caster x 4th level spell x 2000 x 1.5= 84,000 gp.

[Kioran]

I'm looking at buying a custom magic item for a game and wanted to be sure I had done my math correctly for the magic item guidelines.

My intention is to gain a pair of boots of expedious retreat. If I wanted to get a pair of command word activated boots that worked 3/times a day the math would be as follows:

(Spell level x caster level x 1800) [for the base price] / 1.66 [for the charges per day]

If i wanted it to last 2 mins at a time, I need a second level caster, so it would work out to be:

(1 x 2 x 1800) / 1.66 = 2169 gp

If on the other hand, I wanted continous expedious retreat boots, the math is:

spell level x caster level x 2000 x 2 [duration in mins modifier] or

1 x 1 x 2000 x 2 = 4000 gp


So is my math right?

Your math on command-word items is off. It´s:

SL*CL*daily uses/5*1800 GP

for a 3/day expeditious retreat boots which work for 2 minutes, it´d be

1*2*3/5*1800 = 2160 GP

Cheers.

[Chronos]

You could triple the price of lesser boots of striding, but that would be too low still, as DnD prices usually rice exponentially rather than linearly (look at magic weapon bonus price progressions instead).

Nitpick: It's a quadratic progression, not exponential. A quadratic progression is proportional to bonus squared, while an exponential progression would be proportional to something raised to the bonus power. I don't think there's anything in 3rd edition D&D (at least, not in the core rules) which follows an exponential progression, but most of the experience point tables in 2nd edition did, more or less.

And just a reminder to anyone who's trying to find a definitive result from what the guidelines say: There are multiple sets of guidelines in that section, and they don't necessarily give the same price. Yes, there's a formula involving the level of the spell to be simulated, but there's also a guideline to compare it to similar existing items. There can be very large differences between the two, if the relevant spell normally has a very short duration (as with True Strike), or if the ability granted by the item is useful outside of combat (as with the boots discussed here, or a widget of Cure Minor Wounds at will).

[TheElfLord]

Your math on command-word items is off. It´s:

SL*CL*daily uses/5*1800 GP

for a 3/day expeditious retreat boots which work for 2 minutes, it´d be

1*2*3/5*1800 = 2160 GP

Cheers.

Divide by (5 divided by charges per day)

The SRD says otherwise. 5 divided by the charges per day is 5/3 not 3/5.


Thanks for the input. I think part of the problem is that since you are making a continous item, you can just use the caster level you need to cast the spell, or 1 in the case of a first level spell. This messes with the math because 1 times 1 is only 1.

I think what I am going to do is base it off the longstrider spell instead. That would yield 2000 gp for +10, and by squaring the number of the bonus, 3 it would come up with 18,000 gp for +30.

[Talic]

The SRD says otherwise. 5 divided by the charges per day is 5/3 not 3/5.


Thanks for the input. I think part of the problem is that since you are making a continous item, you can just use the caster level you need to cast the spell, or 1 in the case of a first level spell. This messes with the math because 1 times 1 is only 1.

I think what I am going to do is base it off the longstrider spell instead. That would yield 2000 gp for +10, and by squaring the number of the bonus, 3 it would come up with 18,000 gp for +30.

Pretty sure that's a typo, as that would make a device usable 100x a day cheaper than one usable 1x per day.

Nitpick: It's a quadratic progression, not exponential. A quadratic progression is proportional to bonus squared, while an exponential progression would be proportional to something raised to the bonus power. I don't think there's anything in 3rd edition D&D (at least, not in the core rules) which follows an exponential progression, but most of the experience point tables in 2nd edition did, more or less.

Carrying capacity modifiers for size, number of legs come to mind. It's how you can get characters with insane medium loads for hulking hurler.

[Kioran]

The SRD says otherwise. 5 divided by the charges per day is 5/3 not 3/5.

However, that is a classic example of the example and table contradicting the written text. It´s not a real contradiction though - it´s just a matter of different expression of the math. You divide by 5/2, I multiply by 2/5. Let´s play this out with one item, to demonstrate.

"Healbot in a suitcase"

"A small suitcase which, upon command word, opens, releases a tiny construct which casts cure light wound(caster lvl 1) and disappears into the suitcase again"

Now the base price for this item is CL*SL*1800, times the factor based on daily charges. Incidentally, it is 1800.

Now let us do the math for 2 charges:

My solution: 2/5*1800, meaning the item costs 720 for two charges

Your solution: 1800/ 5/2 =1800 / 2.5 = 720.

Yihaidiho. Now one could roll all that into a more elegant solution that does produce round numbers because there´s no rounding error you have in your first post:

SL*CL*360*daily charges. Hooyah!