Estimated Diving Weight Calculator
This calculator determines the estimated diving weight needed for proper buoyancy.
MOD or Maximum Operating Depth
Enter the gas percentage, fraction or FO2 either in % or in decimal 0.XX. You can then choose the desired PO2.Gas oxygen content
Best gas mix
Enter the depth and select the unit. Then select a PO2.Enter the depth
To convert from one system of unit to anotherConvert length
END or Equivalent Narcotic Depth
Enter the depth and select the units. Enter Helium content in fraction eg: 0.40 or in percentage eg: 40.Depth
EAD or Equivalent Air Depth EAD
SAC and RMV
To calculate the SAC or surface Air Consumption you will need to calculate the number of bar used.Average depth
Lift bag required gas
Enter the weight of the object and its volume. Then pick the type of water.Volume of the object
Tank gas content
To calculate the total volume of gas in a tank according to the pressure and size.Enter tank internal volume
Calculate required gas
Calculate the required gas volume for the bottom time of a dive. It does not integrate ascent consumption and is used only for informative purpose.Bottom depth
We think it helps to understand the factors involved rather than just blindly piling on or taking off the lead. So why not break it down to find out why you need to carry the weight you do, and what specifically you are counterbalancing. By deconstructing your buoyancy status, you know exactly where your counterweight needs are greatest, and that might reveal ways to reduce the amount of weight you ultimately have to carry. Here’s how.
How to use Scuba Diving Weight Calculator
STEP 1: Calculate for Your Body
How much weight do you need to make your body neutral? Take a few weights into the water wearing just a swimsuit. You will be perfectly weighted when you can hang motionless with half a breath, and sink when you exhale. (Using a snorkel can make this test easier.)
Tip for Shaving Ballast Weight: Lose weight. Also, work to turn your fat to muscle. Fat mass is a lot more buoyant than muscle mass, so any fat you can convert to muscle will lower your buoyancy deficit.
STEP 2: Calculate for Your Exposure Suit;
Wearing your exposure suit, get into the water and repeat the procedure outlined in Step 1. Then take the total amount of weight required to get neutral, subtract Step 1’s total, and you’ll have the net buoyancy budget for your exposure suit.
Tip for Shaving Ballast Weight: If water conditions permit, cut down on the thickness of your wetsuit. A wetsuit can have one to two kilograms of buoyancy for every millimetre of thickness. If you wear a neoprene drysuit, consider that compressed or crushed neoprene suits have much less buoyancy than standard neoprene. If you wear a fabric drysuit, remember that thinner undergarments have much less buoyancy than the puffy stuff.
STEP 3: Calculate for Your BCD
BCDs can be a huge source of inherent buoyancy, especially the older, full-featured models that have lots of traditional-style padding. It used to be common for BCs to carry upwards of two kilograms plus of inherent buoyancy, which means, of course, that you need two kilograms plus of extra lead on your weight belt to compensate for it. Fortunately, most modern BCs carry much less inherent buoyancy.
To test your BCD’s inherent buoyancy, submerge it while venting all exhaust valves to bleed air from the bladder. Knead the padding in the shoulders and backpad and behind the pockets to release air bubbles. Slowly rotate the BC to enable any trapped air to escape. Be patient, allow plenty of time for water to displace the air in the material. When you stop seeing bubbles, release the BC into the water column. If it heads to the surface you’ve got some inherent buoyancy to deal with. Add weights until the BC will hang neutrally buoyant in the water. Then count up how many weights it took to get there and you’ll have your number.
Tip for Shaving Ballast Weight: Buy a modern BC. Models that have come onto the market within the last three or four years carry, on average, from a half to one kilogram of inherent buoyancy, and some carry none at all. Note: Most manufacturers don’t provide the inherent buoyancy of their BCs.
STEP 4: Calculate for Your Cylinder
The buoyancy characteristics of cylinders vary widely. For example, a standard Catalina S80 aluminium tank weighs 14.3 kg (31.6 lb) empty. It is 0.8 kg (1.7 lb) negatively buoyant when full, and 1.2 kg (2.7 lb) positively buoyant at 35 bar (500 psi). That’s a two kilogram buoyancy differential between the beginning of a dive and the end of a dive. Of course, this needs to be dealt with by adding extra ballast weight.
A steel cylinder, on the other hand, tends to start off negatively buoyant and stay that way. For example, a 232 bar 12.2 litre Faber tank weighs 12.9 kb (28.4 lb) empty. (Yes, the steel cylinder weighs LESS than the aluminium cylinder because the walls of the aluminium cylinder have to be thicker.) This steel cylinder is about 4.25 kg (9.4 lb) negative when full and 0.75 kg (1.7 lb) negative when empty. That’s a 3.5 kg buoyancy differential between the beginning of a dive and the end of a dive. But it’s two kilograms of lead you won’t need compared to using the aluminium S80 cylinder.
Tip for Shaving Ballast Weight: Switch from an aluminium cylinder to a steel cylinder. A properly-weighted diver who goes from an aluminium S80 to, say, a steel 12.2 litre cylinder can usually take two kilograms off their weight belt.
STEP 5: Calculate for Everything Else
Gather your regulators, gauges, knife, fins and any other items you regularly dive with, place them in a neutrally buoyancy mesh bag, and submerge it. The goal here is primarily to see if the total package is positively buoyant. If it is, add some weight until it becomes neutral. If it’s negative it probably won’t be by much, so consider it a ballast slush fund. It’s not working against you, and that’s all that matters.
STEP 6: Put it All Together
Add it all up. This should be very close to your target ballast weight requirements, and it should also give you a clear picture of where your biggest buoyancy challenges lie. To double-check your calculations, gear up with all the components you measured separately, get back into the water and repeat Step 1. If the above scenario played out like it’s supposed to, you should be floating at eye or forehead level in a relaxed position. When you exhale you should start to slowly sink. If not, you couldn’t be more than a pound or so off your target. Make the final adjustment and go diving.