function calculateCoxDrops() {
var pointsInput = document.getElementById("coxPoints");
var raidsInput = document.getElementById("raidCount");
var resultsDiv = document.getElementById("coxResults");
var points = parseFloat(pointsInput.value);
var raids = parseInt(raidsInput.value);
if (isNaN(points) || points < 0) {
alert("Please enter a valid amount of points.");
return;
}
if (isNaN(raids) || raids 1) chancePerRaid = 1;
// Twisted Bow Weighting: 2 / 65 (Standard Unique Table Weight)
var tbowWeight = 2 / 65;
var tbowChancePerRaid = chancePerRaid * tbowWeight;
// Cumulative Probability: 1 – (1 – p)^n
var noPurpleChance = 1 – chancePerRaid;
var chanceAtLeastOnePurple = 1 – Math.pow(noPurpleChance, raids);
var noTbowChance = 1 – tbowChancePerRaid;
var chanceAtLeastOneTbow = 1 – Math.pow(noTbowChance, raids);
// Expected Value
var expectedPurples = chancePerRaid * raids;
// Formatting output
document.getElementById("resPerRaid").innerHTML = (chancePerRaid * 100).toFixed(4) + "% (1/" + Math.round(1/chancePerRaid) + ")";
document.getElementById("resTbowRaid").innerHTML = (tbowChancePerRaid * 100).toFixed(5) + "% (1/" + Math.round(1/tbowChancePerRaid) + ")";
document.getElementById("resKcLabel").innerHTML = raids;
document.getElementById("resKcLabel2").innerHTML = raids;
document.getElementById("resTotalPurple").innerHTML = (chanceAtLeastOnePurple * 100).toFixed(2) + "%";
document.getElementById("resTotalTbow").innerHTML = (chanceAtLeastOneTbow * 100).toFixed(2) + "%";
document.getElementById("resExpected").innerHTML = expectedPurples.toFixed(2);
resultsDiv.style.display = "block";
}
Understanding Chambers of Xeric Drop Rates
The CoX Drop Rate Calculator is designed to help Old School RuneScape (OSRS) players estimate their likelihood of receiving unique loot from the Chambers of Xeric. Unlike traditional RNG drops that are static (e.g., 1/128), CoX uses a points-based system where your participation directly influences your luck.
How the Points System Works
In the Chambers of Xeric, every point you or your team earns contributes to the overall chance of seeing a purple light (a unique item) at the end of the raid. The general consensus within the OSRS community and confirmed mechanics indicate the following formula:
The Golden Number: Approximately 8,675 points equates to a 1% chance of a unique item.
100% Chance: To guarantee a unique (statistically speaking, though caps apply), a team would need roughly 867,500 points.
Personal vs. Team: If you are raiding in a team, the "Drop Chance" is calculated based on total party points to determine if a unique drops. If a unique is rolled, the specific player who receives it is determined by their individual contribution to the total points.
Unique Loot Table Weights
Once the game decides a unique item has dropped (the "Purple Light"), a secondary roll determines exactly which item you receive. This is based on a weighting system. The total weight of the standard unique table is 65.
The Twisted Bow (T-Bow) is the most coveted item from the raid. With a weight of 2 out of a total table weight of 65, the chance of a purple being a Twisted Bow is approximately 1/32.5 (or roughly 3.07%).
To calculate the raw chance of receiving a Twisted Bow per raid, you multiply your chance of getting a purple by this weighting. For example, if you finish a solo raid with 30,000 points (~3.45% chance of purple), your chance of a T-Bow is 3.45% × 3.07% ≈ 0.106% per raid, or roughly 1 in 940 raids.
Using the Calculator
Enter your average points per raid to see your specific odds. "Standard" solo raids usually yield between 30,000 and 32,000 points if you do not die. Team raids vary significantly based on size, efficiency, and scaling. Use the "Number of Raids" field to see your cumulative probability of obtaining items over a long grind.