New Free SAC and RMV Calculator for Scuba Divers

How long will your air last? It's one of the most useful questions a diver can ask, and today it just got easier to answer.

We're happy to announce the DiveHub SAC and RMV calculator. It's live now, it's completely free, and anyone can use it. You don't need a DiveHub account, and you don't need to sign up for anything.

Try the SAC and RMV calculator

What are SAC and RMV?

SAC (surface air consumption) is how much cylinder pressure you use each minute, scaled to the surface. RMV (respiratory minute volume) is how much gas you breathe each minute, also scaled to the surface.

Because gas is compressed by the water around you, you use more of it the deeper you go. SAC and RMV take the depth out of the picture, so you can compare a shallow reef dive with a deeper wall dive. RMV is a volume, so it stays the same whichever cylinder you dive with.

What the calculator does

• Works out your SAC and RMV. Enter your start and end pressures, your average depth and your time at that depth, then choose your cylinder.
• Shows its working. See the absolute pressure, the pressure used and the free gas used, so you can follow every step.
• Metric or imperial. Use bar, metres and litres, or psi, feet and cubic feet.
• Pick your cylinder. Choose a common cylinder size, or enter your own custom size.
• Plans your gas. Use your RMV to estimate how long your gas will last at a planned depth, after holding back a reserve.
• Gentle sense checks. If a number looks unusual, such as a very deep depth or a very high pressure, the calculator lets you know so you can check it.
• Copy your result. Copy the answer with one click to paste into your logbook or share with your buddy.

Private by design

The calculator runs entirely in your browser. Nothing you enter is sent anywhere, so your numbers stay with you.

Why know your own numbers?

Many recreational divers breathe roughly 12 to 25 litres per minute while relaxed at depth. But your own figure matters more than an average. Knowing it helps you:

• Plan your dives with a realistic idea of how long your gas will last.
• Choose a sensible reserve for the dive you have in mind.
• See your progress as your breathing becomes calmer and your buoyancy improves.
• Spot changes when new equipment, cold water or a strong current pushes your consumption up.

Try it over several dives and use the higher figures when you plan.

A quick note: the calculator gives estimates for information only. It uses one average depth for the whole time, and it doesn't replace your training, your dive computer or a proper dive plan. Always plan your reserves with your buddy.

Keep your numbers with your dives

Your pressures, depths and times are already part of your dive log. Log your dives in DiveHub, or import them from your dive computer, and your air consumption data is always close to hand.

Try it now

Head to the SAC and RMV calculator, enter your last dive, and see what your numbers look like. It's free, it's fast, and it's there whenever you need it.

We'd love to hear what you think, and which tools you'd like to see next.