What is SAC rate in scuba diving?

SAC (Surface Air Consumption) rate is the volume of breathing gas a diver consumes per minute, normalized to surface pressure (1 bar / 1 atm). It removes the effect of depth so you can compare consumption across dives and use it to plan gas needs at any depth. A typical recreational diver uses 15–20 L/min (0.5–0.7 cu ft/min). SAC and RMV (Respiratory Minute Volume) are often used interchangeably; both express liters per minute at surface pressure.

How do I calculate how long a scuba tank will last?

Bottom time (minutes) = Usable gas volume (L) ÷ (SAC × absolute pressure at depth). Absolute pressure = depth in metres ÷ 10 + 1. Usable gas = (fill pressure − reserve pressure) × tank water volume. For example, a 12 L tank at 200 bar with a 50 bar reserve gives (200−50)×12 = 1800 L usable. At 20 m depth (3 bar absolute) with a SAC of 18 L/min, bottom time = 1800 ÷ (18×3) = 33 minutes.

How many scuba tank fills do I need for a liveaboard trip?

It depends on your SAC rate, tank size, dive depths, and whether one tank per dive is sufficient. If your gas duration is less than your planned bottom time, you may need a larger tank or a top-off. Multiply dives per day by trip days by tanks per dive to get total fills. For example, 3 dives/day × 7 days × 1 tank = 21 fills minimum — more if you run double tanks or need top-offs.

What does nitrox cost compared to air at a dive shop?

Air fills at a dive shop typically run $5–$20 per fill in the US. Nitrox (enriched air) usually adds a surcharge of $5–$15 per fill, or shops offer an unlimited nitrox fee of $30–$50 for a whole trip. Prices vary widely by region and shop. Use the trip planner to enter your local prices and see the total cost difference between air and nitrox across all planned dives.

How do I measure my SAC rate?

On a dive at a steady depth, note your start pressure, dive for a known time (at least 10 minutes at constant depth and exertion), then record end pressure and average depth. Formula: SAC (L/min) = (P_start − P_end) × tank_volume_L ÷ (dive_time_min × (depth_m÷10 + 1)). Use this planner's SAC calculator tab to compute it from any past dive log entry.

Scuba Dive Trip Gas & Fill Cost Planner

Calculate your SAC/RMV · per-dive tank duration · fills needed for your trip · total gas budget

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🪣 Cylinder

Preset cylinder

Tank water volume (L)

Internal water capacity of the cylinder

Fill pressure (bar)

Reserve pressure (bar)

Gas kept back for ascent + safety stop (typically 50 bar)

📐 Dive Profile

Planned max depth (m)

Your SAC / RMV rate (L/min)

Typical recreational diver: 15–20 L/min. Use SAC tab to calculate yours.

Desired bottom time (min)

Ascent rate (m/min)

PADI recommends no faster than 18 m/min; 9 m/min is conservative

Safety stop depth (m)

Safety stop duration (min)

📊 Single Dive Results

Method (DAN / PADI gas planning standard):
Abs. pressure (ATA) = depth ÷ 10 + 1 Usable gas (L) = (fill_P − reserve_P) × tank_vol Gas at depth (L/min) = SAC × ATA Bottom time (min) = usable gas ÷ gas_at_depth Ascent gas (L) = SAC × (depth÷2÷10+1) × (depth÷ascentRate) Safety stop gas (L) = SAC × (stopDepth÷10+1) × stopDur Source: Divers Alert Network – Estimating Your Air Consumption

Scuba Dive Trip Gas & Fill Cost Planner

Cylinder & Dive Profile

Dive Results

Trip Gas Budget

Estimates for planning guidance only. Always dive within your training and certification. Source: Divers Alert Network gas planning method. Generated: supreminders.com/scuba-dive-trip-gas-fill-cost-planner.html

How to Use This Scuba Dive Trip Gas Planner

This tool covers the complete gas planning workflow — from calculating your SAC/RMV rate to budgeting fill costs for a full dive trip — all in one place.

Step 1 — Set Your Cylinder

Select a preset (AL80, 12 L steel, 15 L steel) or enter custom values. The AL80 (11.1 L water volume, 207 bar) is the standard tank in most dive shops worldwide. European steel 12 L tanks at 200 bar are common on liveaboards in Asia, the Red Sea, and the Pacific.

Step 2 — Find Your SAC Rate

Use the SAC Calculator tab to compute your Surface Air Consumption rate from any past dive. Enter your start/end pressure, dive time, and average depth from your dive computer log. A typical recreational diver uses 15–20 L/min; experienced divers often achieve below 15 L/min. Hit "Use this SAC" to send the result automatically to the Dive Planner and Trip Budget.

Step 3 — Check Your Dive Profile

Enter your planned max depth, desired bottom time, and ascent details. The planner calculates whether one tank is enough, how much gas you actually need (including ascent and safety stop), and how much reserve you will have. A green result means you have comfortable margin; amber means you are pushing the limit; red means you will run out of usable gas before your planned bottom time.

Step 4 — Build Your Trip Budget

In the Trip Budget tab, enter your dive days, dives per day, tanks per dive, and local fill prices. Choose between air, per-fill nitrox surcharge, or an unlimited nitrox trip fee. The tool outputs total fills, total gas cost, gear rental, and a per-dive breakdown you can print or export as a CSV.

When and Why to Use This Tool

Use it before booking a liveaboard trip to estimate your gas bill and confirm one tank is enough per dive. Use it to decide whether buying a larger cylinder is worthwhile for your SAC rate and typical dive depths. Use the SAC tab after every dive trip to track whether your air consumption is improving over time.

Frequently Asked Questions

What is SAC rate and why does it matter?

SAC (Surface Air Consumption) rate — also called RMV (Respiratory Minute Volume) — is the volume of breathing gas you consume per minute, normalised to surface pressure. Because you breathe proportionally more gas molecules at depth, SAC removes the depth variable so you can compare consumption across any dive and use one number to plan gas needs at any depth. A typical recreational diver uses 15–20 L/min; experienced divers often get below 15 L/min. Your SAC rate improves over time as your buoyancy control and relaxation improve underwater.

How long will a scuba tank last at 20 m (66 ft)?

A standard AL80 (11.1 L, 207 bar, 50 bar reserve) provides about 1,730 L of usable gas. At 20 m, absolute pressure is 3 ATA. For a diver with a SAC of 18 L/min, gas consumption at 20 m is 54 L/min, giving a bottom time of approximately 32 minutes — before including ascent gas. A diver with a lower SAC of 13 L/min gets around 44 minutes. Use the Dive Planner above with your personal SAC for an accurate result.

How many tank fills do I need for a 7-day liveaboard?

A typical liveaboard offers 3–4 dives per day. Over 7 days that is 21–28 dives. If you dive single-tank, you need 21–28 fills. If your gas duration falls short of your planned bottom time, you may need to top off, effectively increasing fill count. Enter your specific trip parameters in the Trip Budget tab to get an exact count and cost.

Is nitrox worth the extra cost for a dive trip?

Nitrox reduces nitrogen loading, extending no-decompression limits and potentially reducing post-dive fatigue — particularly valuable when doing 3–4 dives per day. The per-fill surcharge is typically $5–$15, or many liveaboards offer an unlimited nitrox fee of $30–$50 for the whole trip. If you are doing 20+ dives, the per-fill model usually costs more than the flat trip fee. The Trip Budget tab calculates both so you can compare.

Why does my dive computer show a different average depth than max depth?

Most dives follow a profile where you descend, spend time at depth, then ascend — so your average depth is significantly shallower than max depth, often by 30–50%. For SAC calculation, average depth is more accurate than max depth because it reflects your actual gas consumption over the whole dive rather than just the deepest point. Your dive computer records this automatically — always use the average depth figure from your log for SAC calculations.

What is a good reserve pressure to keep?

The most widely taught approach for recreational diving is to end the bottom phase of your dive with a reserve sufficient to cover ascent gas plus the safety stop gas plus an emergency buffer. A common rule of thumb is 50 bar (metric) or approximately 500–700 psi (imperial) as the minimum pressure at which you begin your ascent. Technical and overhead divers use more complex rock-bottom gas calculations. This planner uses your specified reserve as the planned end-of-dive pressure; all usable gas above this is available for the bottom phase.

Method & disclaimer: Calculations use the standard recreational gas planning method published by Divers Alert Network (DAN) and taught by PADI/SSI/BSAC. Seawater density: 1025 kg/m³ (10 m depth ≈ 1 bar). Assumes constant depth for bottom phase. Results are estimates for planning guidance only — not a substitute for dive training, a dive computer, or agency dive tables. Always dive within your certification limits.