How do you calculate tank boil-off rate?

Divide the boil-off liquid equivalent by the starting usable inventory and multiply by 100. With 8 gallons lost from a 250-gallon starting inventory, the boil-off rate is 3.2% per period.

What is a normal LNG boil-off rate?

Large well-insulated LNG tanks run roughly 0.05-0.15% per day, while small vacuum-jacketed vessels lose more on a percentage basis because of their higher surface-to-volume ratio. Always compare against your own tank's baseline and rated NER, not a generic figure.

Why does boil-off rate rise as the tank empties?

The heat leak is roughly constant, but it's divided by a shrinking inventory, so the same gallons of boil-off become a larger percentage. That's why low-fill tanks show higher rates and why you should note the fill level when trending boil-off.

What does it mean if boil-off exceeds the target?

It signals the tank is losing more product than your spec allows and is the first sign of degrading vacuum insulation or a passing relief valve. Trend several readings; a steadily climbing rate at similar fill levels points to insulation breakdown that needs inspection.

Is boil-off rate the same as normal evaporation rate (NER)?

They measure the same loss but NER is the manufacturer's rated daily loss for a full, settled tank under standard conditions. Your measured boil-off rate compared against NER tells you whether the tank is still performing to spec.

Cryogenic Storage & LNG Equipment calculator

Tank Boil-Off Rate Calculator

Tank boil-off rate is the share of a cryogenic or LNG tank's liquid inventory lost to vapor over a period as heat leaks through the insulation. Plant engineers and fuel-station operators track it because boil-off is both a product loss and a pressure-management problem — vapor that vents is money gone, and vapor that doesn't vent raises tank pressure. The rate normalizes loss against starting inventory so a 250-gallon and a 25,000-gallon tank can be compared on equal footing. Watching this rate over time is the cleanest early warning that vacuum insulation is degrading.

What this calculator does

Calculate cryogenic tank boil-off as a percent of starting liquid inventory so operators can judge holding performance, vent loss, and refill risk.
Use it when tank boil-off rate in cryogenic storage and lng equipment needs a clean rate and gap-to-target you can put on a tier board.
It computes boil-off rate as vented liquid equivalent divided by starting inventory, times 100, and compares it against a target maximum.

Formula used

Tank boil-off rate = boil-off or vented liquid equivalent ÷ starting usable liquid inventory × 100
Boil-off above target = measured boil-off rate − target maximum boil-off rate

Inputs explained

Boil-off or vented liquid equivalent:
Starting usable liquid inventory:
Target maximum boil-off rate:

How to use the result

Use it for routine boil-off monitoring on LNG, liquid nitrogen, oxygen, or argon storage, and to flag tanks whose insulation may be failing.
Rate alone doesn't isolate the cause — high ambient heat, frequent valve cycling, low fill level, and lost vacuum all raise boil-off, so a high reading needs follow-up to diagnose.

Current U.S. benchmarks

Global copper trades at $13,484 per tonne (IMF via FRED, May 2026), up 41.5% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate tank boil-off rate? Divide the boil-off liquid equivalent by the starting usable inventory and multiply by 100. With 8 gallons lost from a 250-gallon starting inventory, the boil-off rate is 3.2% per period.
What is a normal LNG boil-off rate? Large well-insulated LNG tanks run roughly 0.05-0.15% per day, while small vacuum-jacketed vessels lose more on a percentage basis because of their higher surface-to-volume ratio. Always compare against your own tank's baseline and rated NER, not a generic figure.
Why does boil-off rate rise as the tank empties? The heat leak is roughly constant, but it's divided by a shrinking inventory, so the same gallons of boil-off become a larger percentage. That's why low-fill tanks show higher rates and why you should note the fill level when trending boil-off.
What does it mean if boil-off exceeds the target? It signals the tank is losing more product than your spec allows and is the first sign of degrading vacuum insulation or a passing relief valve. Trend several readings; a steadily climbing rate at similar fill levels points to insulation breakdown that needs inspection.
Is boil-off rate the same as normal evaporation rate (NER)? They measure the same loss but NER is the manufacturer's rated daily loss for a full, settled tank under standard conditions. Your measured boil-off rate compared against NER tells you whether the tank is still performing to spec.

Last reviewed 2026-05-12.