Published unique formula · current values stay editable
OSRS Barrows Loot Calculator
Model equipment odds from the number of brothers killed, then build a transparent GP scenario from current values, the rune-only Hard Diary benefit, and your measured full chest cycle.
Build a sourced Barrows chest scenario
Brother count drives the published equipment-roll formula. GP values start at zero because prices and non-unique chest value change; enter a dated source or personal average instead of relying on the retired September 2025 snapshot.
A provenance label only; it does not change hidden values.
Record a GE timestamp, Wiki calculator output, or your own chest-log window.
The OSRS Wiki formula supports 1 through 6; each kill also adds one reward roll.
Used for cumulative any-equipment and named-piece scenarios.
Measure travel, combat, tunnels, looting, banking, and reset—not only the fights.
Supplies, charges, tablets, and other costs from the same measurement window.
Average the current values of the four pieces for every brother killed; do not include unavailable sets.
Enter only the rune component so the published 50% quantity bonus is not applied to coins, racks, keys, or equipment.
A user-supplied average for all remaining chest value. Reward Potential is not guessed.
Equipment from an un-killed brother is unavailable; the named-piece probability becomes zero.
The published benefit is 50% more runes. It does not multiply unique or other reward value.
Any unique per opening
6.6642%
Named piece per opening
0.2859%
Any unique in plan
99.8989%
Named piece in plan
24.9006%
Formula and value boundary
- Reward rolls per opening
- 7
- Equipment chance per roll
- 0.9804%
- Expected unique pieces per run
- 0.06863
- Expected unique value per run
- 0 GP
- Diary-adjusted rune component
- 0 GP
- Gross expected value per run
- 0 GP
- Net expected value per run
- 0 GP
- Measured completions per hour
- 30
- Net expected GP per hour
- 0 GP
For N brothers, the source gives p = 1 ÷ (450 − 58N) per roll and N + 1 rolls. Any-unique chance is 1 − (1 − p)^(N+1). A named available piece is selected symmetrically from 4N pieces, giving (N+1) × p ÷ (4N) per opening. Repeated-run output assumes the same setup each time.
The corrected equipment model
The OSRS Wiki Barrows chest mechanics give the chance of a Barrows equipment piece on one reward roll as 1 ÷ (450 − 58N), where N is the number of brothers killed. A chest starts with one roll and gains one additional roll for each brother killed, up to seven.
With six brothers killed, the per-roll chance is 1/102 and the chest has seven rolls. Therefore, the chance of at least one equipment piece is 1 − (101/102)^7, approximately 6.67%. An earlier version of LootCalc incorrectly treated 1/102 as the unconditional chance for each of 24 pieces and summed them to roughly 23.5%. That interpretation was wrong and has been removed.
Named-piece probability
Only equipment associated with killed brothers is available. Four items are added for each killed brother. When an equipment roll succeeds, one available piece is selected uniformly and cannot be selected again on a later roll in that chest. By symmetry, one named available piece has probability (N + 1) × p ÷ (4N). At six brothers this is 7 × 1/2,448, approximately 0.286% per chest, matching the Wiki reward table.
The target checkbox exists because a formula cannot rescue an unavailable item. If the named piece belongs to a brother you skipped, its result is zero even though another set can still drop.
Why the calculator no longer ships price tables
The deleted September 2025 file mixed stale GE-like prices, fabricated common-item probabilities, and a false aggregate equipment rate. Current expected value requires current prices and the player's actual Reward Potential. Rather than imply that one old chest average fits every route, the revised calculator asks for three explicit components:
- the average current value of the equipment pieces available under the selected brother count;
- the average rune component before any diary multiplier;
- the average remaining non-unique value from a dated source or personal log.
The expected number of equipment pieces per chest is (N + 1) × p. Multiplying that by the entered average available-piece value gives the unique component. This is an expectation over many comparable chests, not the likely value of one chest.
Apply the diary to runes only
The Morytania Hard Diary reward is 50% more runes from the Barrows chest. The old code applied 10% to both runes and bolt racks while nearby copy claimed 50%, creating a code/content contradiction. The new model applies a factor of 1.5 only to the rune-value input.
Measure a complete route
Time from the first brother to the chest is not a full cycle. Include travel, crypt entry, all fights, tunnel navigation, looting, banking, restoration, and the return to a comparable start state. Measure several real cycles and use the mean or median that answers your question. Enter costs from the same window so net GP per hour does not combine fast-run time with a different supply setup.
Reward Potential remains outside the unique formula
Reward Potential changes other chest items, not the equipment-roll formula. Its full table is more complex than a single percentage, so this page does not infer it from a route label. Record the observed potential and use a matching non-unique average. For an Iron account, substitute personal valuations only if they answer your stated decision; do not present them as market prices.
Frequently asked questions
What is the Barrows equipment chance with all six brothers killed?
The published per-roll chance is 1/102 and the chest receives seven rolls. The chance of at least one equipment piece is 1 minus (101/102) to the seventh power, about 6.67% per chest.
What is the chance of one named Barrows piece?
With all six relevant brothers killed, 24 pieces are available and the Wiki table expresses a named piece as 7 × 1/2,448, about 0.286% per chest. If its brother was not killed, that piece is unavailable.
Why are GP inputs zero by default?
GE prices, reward potential, route costs, and chest averages change. Enter current values from a dated source or your own log instead of treating an old price snapshot as current.
How is the Morytania Hard Diary modeled?
It multiplies only the user-entered rune component by 1.5, matching the published 50% more runes reward. It does not increase equipment, coins, racks, keys, or every chest value.
Does cumulative probability guarantee a drop?
No. It is the complement probability for repeated chests under the same entered setup. Independent outcomes can still produce a longer dry streak.