OSRS Barrows Tools

What the primary mechanics support

The OSRS Wiki Barrows chest page publishes the equipment chance on each reward roll as 1 ÷ (450 − 58N), with N brothers killed. The chest has one initial reward roll and one extra roll for each brother, up to seven. Killed brothers also determine which sets can be selected.

These facts are sufficient for any-equipment and named-piece probability. They are not sufficient for a universal chest GP value. Non-unique rewards depend on Reward Potential, item quantities, and current valuations, while route profit depends on the player's measured speed and supplies.

Correct six-brother interpretation

At six brothers, one reward roll has a 1/102 equipment chance. Seven rolls do not mean that each of 24 pieces independently has a 1/102 chance. The correct any-equipment result is 1 − (101/102)^7, approximately 6.67% for the chest. For one named piece among all 24 available pieces, the Wiki table gives 7 × 1/2,448, approximately 0.286%.

This distinction is material. The retired local model summed 24 copies of 1/102 to produce about 23.5%, more than three times the proper any-equipment probability. It also attached invented common-item chances and static prices. Those inputs and their CSV log have been removed.

Build current value from components

1. Choose the number of brothers killed and verify the named target is available.
2. Average current values across the four pieces for each killed brother, using one dated price source.
3. Record the average rune value before diary effects from a matching Reward Potential setup.
4. Record other non-unique value separately so the diary cannot inflate it.
5. Measure the complete chest cycle and costs over the same route window.

The calculator multiplies expected equipment count by the entered mean piece value. It then adds the rune and other components, subtracts cost, and scales the result by measured chests per hour. This is transparent expected-value arithmetic, not a live market feed.

Hard Diary boundary

The Morytania Hard Diary grants 50% more runes from the chest. It does not say 10%, does not require the Elite tier, and does not multiply every reward. The model therefore applies 1.5 only to the rune component that the user entered.

Use an empty observation log

A reproducible log can begin with timestamp_utc,brothers_killed,reward_potential,hard_diary,unique_items,rune_value_gp,other_value_gp,cost_gp,cycle_seconds,price_source,notes. Add rows only after real chests. Do not seed the file with sample rewards that could be mistaken for observations. When prices change, preserve the loot quantities and revalue them under a named timestamp rather than rewriting the original event.

Interpret cumulative probability

Repeated-chest probability uses 1 − (1 − p)^n under an unchanged setup. It describes the chance of at least one qualifying result across n chests, not a guarantee or pity system. If brother count changes, split the plan into homogeneous batches and combine their miss probabilities.