RuneScape Wiki


37,486pages on
this wiki
Add New Page
Discuss0 Share
Release date 25 January 2016 (Update)
Rarity Other
Level 1
Experience 0
There may be some use to this stuff, somehow?

Junk is a material used in the Invention skill. Items that can be disassembled have a junk chance, which determines the likelihood of receiving junk as a component. Using the Analyse ability on an item displays a percentage chance of receiving junk from disassembly.

When disassembling an item, the first roll determines whether or not junk will be received. A second roll will determine what material is given if not junk.

Possible perksEdit

As material for a gizmo shell, Junk does not grant any possible perks.


Item Skill Materials
Junk refiner Junk refiner22 Invention


The percentage of junk can be reduced through research.

Research Level Inspiration cost
Junk chance reduction 1 34 750
Junk chance reduction 2 49 900
Junk chance reduction 3 64 1,750
Junk chance reduction 4 69 1,750
Junk chance reduction 5 78 2,300
Junk chance reduction 6 83 4,500
Junk chance reduction 7 91 6,000
Junk chance reduction 8 95 6,000
Junk chance reduction 9 105 11,000


The (base) junk chance of the vast majority of items depends primarily on the item's 'level'. For many items, this is the level to use or obtain the item in some way, for example:

  • Most equipment use the level needed to equip
  • Seeds use the Farming level to plant
  • Logs use the Woodcutting level to cut
  • Runes use the Runecrafting level to make
  • Items that do not have an associated level usually use 1

This level may be distinct from other levels associated with the item, like required levels to earn the item, equipment tier, etc. This level is also used in calculating the item's disassembly experience. An item's level is 1 at a minimum.

Augmented items of equipment level 4 and higher have a junk chance of 0.

There are two distinct cutoff points where the formula for junk chance changes significantly: 75 and 90. In addition, arrows and bolts follow a slightly altered formula.

In the following formulae:

  • J is the base junk chance as a percentage
  • \hat{J} is the junk chance including reduction
  • L is the item level
    • f(L) is a function that maps level to junk chance in the 75–89 range
  • r is the junk chance reduction researched (0 to 9)
    • g(r) is a function that maps the reduction research number to a multiplier
  • All results are truncated to 1 decimal place

As mentioned, there are two cutoff points - creating 3 formulae - for junk chance for most items. This is summarised as follows:

J = \begin{cases}
100 - 1.1 \times L & L < 75 \\
f(L) & 75 \le L < 90 \\
0 & L \ge 90 \\

Where f(L) is given by the following table:

  L   f(L)   L   f(L)   L   f(L)
75 4.2 80 2.3 85 1.0
76 3.8 81 2.0 86 0.8
77 3.4 82 1.7 87 0.6
78 3.0 83 1.4 88 0.4
79 2.7 84 1.2 89 0.3

The best-fitting curve for this data set is approximated as:
f(L) \approx 99.1 - 2.089 \times L + 1.1 \times \left( \frac{L}{10} \right)^2


Ammunition uses the 'under level 75' formula from above, but the level value is halved (and rounded down, but not less than 1).

J_{ammo} = 100 - 1.1 \times \mbox{max} \left ( \left \lfloor \frac{L}{2} \right \rfloor, 1 \right )


Junk chance reduction is a simple multiplier of the base junk chance, given by

\hat{J} = J \times g(r)

where g(r) is given by the following table:

  r   g(r)   r   g(r)
0 1 5 0.91
1 0.99 6 0.88
2 0.97 7 0.86
3 0.95 8 0.83
4 0.93 9 0.80

This means that items with a higher junk chance get a much larger benefit from junk chance reduction than items with a lower junk chance.

See alsoEdit

Ad blocker interference detected!

Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.