Diving Sac Rate Calculator

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Scuba Diving SAC Rate Calculator

Calculate your Surface Air Consumption (SAC) rate and Respiratory Minute Volume (RMV) to better plan your gas management for scuba diving.

Your Gas Consumption Rate

Surface Air Consumption (SAC):
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Respiratory Minute Volume (RMV):
–

Understanding Surface Air Consumption (SAC)

Your Surface Air Consumption (SAC) rate is a critical metric in scuba diving that indicates how much breathing gas you consume per minute, normalized to surface pressure. Knowing this number allows you to plan dives safely, ensuring you have enough gas to complete your dive and handle emergencies.

Why Calculate Your SAC Rate?

  • Gas Planning: Estimate exactly how long a specific tank will last at a specific depth.
  • Benchmarking: Track your improvement as a diver. Lower SAC rates often indicate better buoyancy, trim, and comfort in the water.
  • Tank Selection: Decide if you need a larger tank (e.g., 15L or 100cf) for deeper or longer dives based on your consumption.
  • Buddy Matching: Compare rates with your dive buddy to plan turn-around pressures based on the diver with the highest consumption.

The Formulas Used

This calculator adapts the formula based on the unit system selected:

Metric System Formula

In the metric system, we calculate liters of gas consumed per minute.

  1. Gas Used (Bar): Start Pressure – End Pressure
  2. Total Volume (Liters): Gas Used (Bar) × Tank Volume (Liters)
  3. Pressure at Depth (ATA): (Depth in meters / 10) + 1
  4. SAC (L/min): (Total Volume / Time) / ATA

Imperial System Formula

In the imperial system, divers often look for the Respiratory Minute Volume (RMV) in cubic feet per minute.

  1. Gas Used (PSI): Start Pressure – End Pressure
  2. Pressure at Depth (ATA): (Depth in feet / 33) + 1
  3. SAC (PSI/min): ((Gas Used / Time) / ATA)
  4. Tank Factor: Rated Capacity (cu ft) / Working Pressure (PSI)
  5. RMV (cu ft/min): SAC (PSI/min) × Tank Factor

What is a "Good" SAC Rate?

SAC rates vary significantly based on physical size, fitness, workload, water temperature, and stress levels. However, general benchmarks include:

  • New Diver / High Workload: 20 – 25 Liters/min (0.7 – 0.9 cu ft/min)
  • Average Diver: 14 – 18 Liters/min (0.5 – 0.65 cu ft/min)
  • Experienced / Relaxed: 10 – 13 Liters/min (0.35 – 0.45 cu ft/min)

Tips to Improve Your Air Consumption

  1. Perfect Your Buoyancy: Constant adjustments to your BCD waste air and energy.
  2. Streamline Your Gear: Reduce drag to reduce the effort needed to swim.
  3. Slow Down: Swimming twice as fast requires four times the energy (and air).
  4. Stay Warm: The body burns significant energy to maintain core temperature in cold water.
var currentUnit = 'metric'; function toggleUnits(unit) { currentUnit = unit; var labelTank = document.getElementById('labelTankSize'); var inputTank = document.getElementById('tankSize'); var groupWorking = document.getElementById('groupWorkingPressure'); var labelStart = document.getElementById('labelStartPressure'); var labelEnd = document.getElementById('labelEndPressure'); var labelDepth = document.getElementById('labelDepth'); var startInput = document.getElementById('startPressure'); var endInput = document.getElementById('endPressure'); var depthInput = document.getElementById('averageDepth'); if (unit === 'metric') { // Metric Labels labelTank.innerHTML = 'Tank Water Volume (Liters)'; inputTank.placeholder = 'e.g. 12'; groupWorking.classList.add('hidden'); labelStart.innerHTML = 'Starting Pressure (Bar)'; startInput.placeholder = 'e.g. 200'; labelEnd.innerHTML = 'Ending Pressure (Bar)'; endInput.placeholder = 'e.g. 100'; labelDepth.innerHTML = 'Average Depth (Meters)'; depthInput.placeholder = 'e.g. 15'; } else { // Imperial Labels labelTank.innerHTML = 'Tank Rated Capacity (Cubic Feet)'; inputTank.placeholder = 'e.g. 80'; groupWorking.classList.remove('hidden'); labelStart.innerHTML = 'Starting Pressure (PSI)'; startInput.placeholder = 'e.g. 3000'; labelEnd.innerHTML = 'Ending Pressure (PSI)'; endInput.placeholder = 'e.g. 1500'; labelDepth.innerHTML = 'Average Depth (Feet)'; depthInput.placeholder = 'e.g. 50'; } // Clear result area when switching document.getElementById('resultArea').style.display = 'none'; } function calculateSAC() { // Get Inputs var tankSize = parseFloat(document.getElementById('tankSize').value); var startP = parseFloat(document.getElementById('startPressure').value); var endP = parseFloat(document.getElementById('endPressure').value); var depth = parseFloat(document.getElementById('averageDepth').value); var time = parseFloat(document.getElementById('diveTime').value); // Validation if (isNaN(tankSize) || isNaN(startP) || isNaN(endP) || isNaN(depth) || isNaN(time)) { alert("Please fill in all fields with valid numbers."); return; } if (time <= 0) { alert("Bottom time must be greater than zero."); return; } if (startP <= endP) { alert("Starting pressure must be higher than ending pressure."); return; } var resultArea = document.getElementById('resultArea'); var sacDisplay = document.getElementById('sacResult'); var rmvDisplay = document.getElementById('rmvResult'); var explanation = document.getElementById('explanationText'); if (currentUnit === 'metric') { // Metric Calculation // 1. Gas Used (Bar) var barUsed = startP – endP; // 2. Total Liters Used var litersUsed = barUsed * tankSize; // 3. Pressure at Depth (ATA) var ata = (depth / 10) + 1; // 4. SAC (Liters/min at surface) var sacRate = (litersUsed / time) / ata; // In Metric, RMV and SAC are often used interchangeably as Liters/min // We display the same value sacDisplay.innerHTML = sacRate.toFixed(2) + " L/min"; rmvDisplay.innerHTML = sacRate.toFixed(2) + " L/min"; explanation.innerHTML = "In the metric system, SAC and RMV both represent the volume of gas (liters) breathed per minute at surface pressure. You consumed " + litersUsed.toFixed(0) + " liters of gas during this dive."; } else { // Imperial Calculation var workingP = parseFloat(document.getElementById('workingPressure').value); if (isNaN(workingP) || workingP <= 0) { alert("Please enter a valid Working Pressure for the tank."); return; } // 1. Gas Used (PSI) var psiUsed = startP – endP; // 2. Pressure at Depth (ATA) var ata = (depth / 33) + 1; // 3. SAC (PSI/min) var sacPsi = (psiUsed / time) / ata; // 4. Tank Factor (CuFt per PSI) var tankFactor = tankSize / workingP; // 5. RMV (CuFt/min) var rmv = sacPsi * tankFactor; sacDisplay.innerHTML = sacPsi.toFixed(2) + " PSI/min"; rmvDisplay.innerHTML = rmv.toFixed(2) + " Cu Ft/min"; explanation.innerHTML = "Your SAC is " + sacPsi.toFixed(2) + " PSI/min (specific to this tank size). Your RMV is " + rmv.toFixed(2) + " cubic feet per minute (transferable across different tank sizes)."; } resultArea.style.display = 'block'; }

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