function calculateBuoyancy() {
var weightInput = document.getElementById('diverWeight').value;
var unit = document.getElementById('weightUnit').value;
var suit = document.getElementById('suitType').value;
var water = document.getElementById('waterType').value;
var tank = document.getElementById('tankType').value;
var resultDiv = document.getElementById('scubaResult');
// Validation
if (weightInput === "" || isNaN(weightInput) || weightInput <= 0) {
resultDiv.style.display = 'block';
resultDiv.innerHTML = 'Please enter a valid body weight.';
return;
}
var weightLbs = parseFloat(weightInput);
// Normalize to lbs for calculation logic
if (unit === 'kg') {
weightLbs = weightLbs * 2.20462;
}
var estimatedLead = 0;
// Base Logic (Saltwater Baseline)
// Formulas derived from PADI Peak Performance Buoyancy guidelines
switch (suit) {
case 'skin':
estimatedLead = 2; // Basic harness weight compensation
break;
case '3mm':
estimatedLead = weightLbs * 0.05; // ~5% of body weight
break;
case '5mm':
estimatedLead = weightLbs * 0.10; // ~10% of body weight
break;
case '7mm':
estimatedLead = (weightLbs * 0.10) + 4; // ~10% + hood buffer
break;
case 'dry':
estimatedLead = (weightLbs * 0.10) + 10; // ~10% + heavy undergarment buffer
break;
}
// Adjust for Freshwater
// Freshwater is less dense; you are less buoyant and need LESS lead.
// Approx reduction is 2.5% of body weight relative to saltwater.
if (water === 'fresh') {
estimatedLead = estimatedLead – (weightLbs * 0.025);
}
// Adjust for Tank Characteristics
// Aluminum 80s become buoyant (+2 to +4 lbs) near 500psi. Need extra weight to hold stop.
// Steel tanks stay negative (-2 to -6 lbs). Need less weight.
if (tank === 'aluminum') {
estimatedLead += 3; // Adding weight to compensate for positive buoyancy at end of dive
} else if (tank === 'steel') {
estimatedLead -= 4; // Subtracting weight because tank is heavy
}
// Floor at 0
if (estimatedLead < 0) estimatedLead = 0;
// Calculate Range (+/- 2 lbs)
var minWeight = Math.floor(estimatedLead – 2);
if (minWeight < 0) minWeight = 0;
var maxWeight = Math.ceil(estimatedLead + 2);
// Display Logic
var displayString = "";
if (unit === 'kg') {
// Convert result back to kg
var minKg = (minWeight / 2.20462).toFixed(1);
var maxKg = (maxWeight / 2.20462).toFixed(1);
displayString = minKg + " kg – " + maxKg + " kg";
} else {
displayString = minWeight + " lbs – " + maxWeight + " lbs";
}
resultDiv.style.display = 'block';
resultDiv.innerHTML = 'Recommended Weight Range:' + displayString + '*This is an estimate. ALWAYS perform a proper buoyancy check at the surface before descending.';
}
Mastering Buoyancy: The Ultimate Scuba Weight Calculator Guide
Proper weighting is the holy grail of scuba diving. Carrying too much lead causes drag, increases air consumption, and leads to poor trim. Carrying too little can make it impossible to descend or, more dangerously, cause an uncontrolled ascent during your safety stop. Our Scuba Diving Weight Calculator helps you estimate the correct amount of lead based on your physiology and equipment configuration.
How to Calculate Scuba Weight Needed
While every diver's body composition is unique, buoyancy follows the laws of physics. The amount of weight you need is determined by the volume of water you displace versus your total mass. Several key factors influence this equation:
Exposure Protection (Wetsuits/Drysuits): Neoprene contains nitrogen bubbles that trap air. The thicker the suit, the more buoyant you are. A 7mm wetsuit requires significantly more weight than a 3mm shorty. As you descend, the neoprene compresses, and you become less buoyant (more negative).
Body Weight: Generally, divers need approximately 5-10% of their body weight in lead when wearing a wetsuit. Muscle is denser than fat, so muscular divers often sink more easily and require less lead than divers with higher body fat percentages.
Water Salinity: Saltwater is denser than freshwater (approx. 64 lbs/cu ft vs 62.4 lbs/cu ft). This extra density provides more lift. If you transition from ocean diving to a freshwater lake, you will need to remove approximately 4-7 lbs (2-3 kg) of weight.
Cylinder Type: This is often overlooked. An Aluminum 80 tank starts negatively buoyant but becomes roughly 2-4 lbs positively buoyant as you consume air. You must carry extra weight to offset this "floaty" tank at your safety stop. Steel tanks remain negatively buoyant throughout the dive, allowing you to carry less lead on your belt or BCD.
Pro Tip: The goal is not just to sink; it is to remain neutral at your safety stop (15 ft / 5 m) with 500 psi (35 bar) in your tank.
Performing a Proper Buoyancy Check
Calculators provide a starting point, but they cannot replace an in-water buoyancy check. Follow these steps before every dive, especially when changing gear:
Enter the water wearing all your equipment (mask, fins, tank, weights).
Put your regulator in your mouth and take a normal breath. Hold it.
Deflate your BCD completely.
You should float at eye level. If you sink past your eyes, you are overweighted. If your whole head stays out, you are underweighted.
Exhale. You should sink slowly.
Why Being Overweighted is a Problem
Many new divers wear too much weight "just to be safe." However, being overweighted forces you to inflate your BCD significantly at depth to compensate. This creates a larger surface area, increasing drag and water resistance. You will burn through your air supply faster and struggle to maintain a horizontal trim position. Aim for the minimum weight required to maintain a safety stop with an empty tank.