Leak Rate Calculator
A slow drip from a fitting, a pressure rise in an isolated vacuum chamber, a rooftop unit that needs refrigerant again: three different problems, one shared question. How fast is it leaking? This calculator answers it three ways, with a fluid mode for volume lost over time, a vacuum mode using the pressure-rise method in mbar·L/s, and a refrigerant mode that applies the EPA Section 608 formula and checks the result against the legal repair thresholds.
Quick Answer
A cooling line that loses 25 liters in 5 hours leaks at 5.0000 liters/hour, about 120 liters per day. A 5-liter vacuum chamber rising 0.05 mbar in 50 seconds leaks at 0.005 mbar·L/s. Adding 5 lbs of refrigerant to a 100-lb commercial system 90 days after the last top-off annualizes to 20.28%, which crosses the 20% EPA repair threshold. The calculator above is pre-filled with all three cases, one per tab.
Key takeaways
- Pick the mode by the job, not by the unit: fluid for anything you can collect or meter, vacuum for an isolated chamber, EPA for a refrigerant addition event.
- The EPA mode uses the nameplate full charge and calendar days, and it runs per addition event. A yearly total typed in at once gives the wrong answer.
- The vacuum number counts outgassing as well as holes. A rate that improves over repeated pump-downs is mostly outgassing; a rate that will not move is a real leak.
- At or above an EPA threshold the verdict is repair: 30 days to fix it, or a retrofit or retirement plan inside one year.
- Quick Answer
- How to use the leak rate calculator
- The three formulas, and what each one assumes
- Worked examples for all three modes
- EPA Section 608: thresholds, scope and the repair clock
- Vacuum leak rates: reading a pressure-rise result properly
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the leak rate calculator
Start on the tab that matches your measurement, enter the numbers you actually recorded, and read the verdict line under the main result. Results stay hidden until you click Calculate.
- Fluid leak rate: enter the volume lost and the time it took, choosing the units on both inputs. The result shows the rate in your chosen units, plus what the leak costs per day if it continues. This mode suits water lines, coolant loops, hydraulic seeps and tank losses, and it works for gas volumes too when the volume is big enough to meter. For a leaking garden line, compare the figure with the hose flow rate calculator to see how much of the hose output the leak represents.
- Vacuum leak rate: pump the chamber down, close the isolation valve, and record the starting pressure. Wait, record the ending pressure, and enter the rise in mbar, the chamber volume in liters and the elapsed seconds. The result is in mbar·L/s with a note on where it sits against the typical high-vacuum benchmark of 1×10⁻⁶ mbar·L/s.
- Refrigerant (EPA 608): enter the pounds added at this service visit, the nameplate full charge, and the calendar days since the last addition, then pick the appliance type. The tool annualizes the rate with the EPA formula and states whether the repair threshold is crossed.
Two habits keep all three modes honest. Measure over the longest window you reasonably can, because a slow leak timed over two minutes is mostly stopwatch error. And write the inputs down with the result: a leak rate without its volume, pressure rise and test time cannot be checked later, and for refrigerant work the record is part of the compliance file.
The three formulas, and what each one assumes
Each mode divides an amount of escaped gas or fluid by time, but the amount is measured differently in each field, which is why the units and the verdicts differ.
Vacuum (pressure-rise): Leak Rate = (Chamber Volume × Pressure Rise) ÷ Test Time
EPA refrigerant: Leak Rate (%) = (Refrigerant Added ÷ Nameplate Full Charge) × (365 ÷ Days Since Last Addition) × 100
The fluid formula assumes the leak ran at a roughly steady rate during your window. That is fair for a drip or a seep and shaky for a leak that only opens under pressure cycles, so time the measurement across a full cycle when you can. The vacuum formula, the rate-of-rise method described in vacuum references such as the Agilent vacuum and leak detection reference, assumes the chamber volume is known and the temperature stays put; a chamber warming up during the test inflates the apparent rate. The EPA formula assumes the system was returned to full charge at the last addition, which is why it uses the nameplate charge as the denominator.
Leak rate is not flow rate, and the two tools on this site answer opposite questions. Flow is the movement you designed for; a leak is the movement you did not. When the question is what a pipe or channel delivers on purpose, the flow rate and pressure calculator and the drain flow rate calculator cover that side; this page is only about unintended loss.
Worked examples for all three modes
Every row below is a verified run of the calculator above, including the three pre-filled cases and two extra runs that show the unit conversions and the benchmark logic working.
| Run | Result the tool returns |
|---|---|
| Fluid: 25 liters lost over 5 hours | 5.0000 liters/hour; about 120 liters lost per day |
| Fluid: 10 US gallons over 2 days | 5.0000 gallons/day; about 5 gallons lost per day |
| Vacuum: 5 L chamber, 0.05 mbar rise, 50 seconds | 0.005 mbar·L/s; above the high-vacuum benchmark |
| Vacuum: 10 L chamber, 0.00001 mbar rise, 100 seconds | 1.00e-6 mbar·L/s; within the high-vacuum benchmark |
| EPA: 5 lbs added, 100-lb charge, 90 days, commercial | 20.28%; exceeds the 20% threshold, repair within 30 days |
| EPA: 2 lbs added, 50-lb charge, 365 days, comfort cooling | 4.00%; within the 10% threshold, no mandatory repair |
The fluid example is worth staring at for a second, because the daily figure is what turns a drip into a work order. A leak that looks harmless hour by hour compounds into real volume:
Household leaks behave the same way at smaller scale: the EPA WaterSense guidance on fixing leaks exists because drips that nobody would call an emergency add up to thousands of gallons a year across a building stock.
EPA Section 608: thresholds, scope and the repair clock
The refrigerant mode implements the annualized leak rate in 40 CFR 82.157, the leak repair rule: pounds added divided by the full charge, scaled by 365 over the days since the last addition, times 100. The verdict in the tool follows the same thresholds the regulation sets.
Scope matters as much as the percentage. The Section 608 leak repair duties summarized in the EPA Section 608 refrigerant management regulations apply to appliances with a full charge of 50 pounds or more. From January 1, 2026, the AIM Act HFC management rule extends leak repair duties to HFC appliances of 15 pounds or more, with the same 10%, 20% and 30% category thresholds; the annualized arithmetic this tool runs is the same either way. One behaviour to know before you rely on the verdict: this calculator treats a result at or above the threshold as crossed, so exactly 20.00% on a commercial system returns the repair verdict. Treat an exact-threshold result as a trigger and document it, not as a loophole.
Crossing a threshold starts a clock, not a suggestion. The leak must be repaired within 30 days, follow-up verification testing applies, and a system that cannot be fixed goes onto a retrofit or retirement path inside one year. Comfort cooling is where the 10% line catches people out: a well-meaning top-off on a large rooftop unit is exactly the kind of addition event the rule counts, and sizing questions upstream, such as the load work behind the AC tonnage calculator, do not change the charge figure on the nameplate that this calculation needs.
Vacuum leak rates: reading a pressure-rise result properly
A pressure-rise result is a total gas load, not a hole count: it sums real leaks, permeation through seals and outgassing from the chamber walls. That is why the same chamber can test worse on a humid Monday than it did on Friday.
Run the test the same way every time. Pump down to your usual base pressure, isolate, wait a fixed settling period so the initial surge from outgassing passes, then time the rise over a window long enough for the gauge to move clearly. Repeat the cycle: outgassing falls with each pump-down, a true leak does not. If the rate holds steady across cycles, start hunting with a helium detector at the flanges and feedthroughs; if it keeps dropping, your chamber is drying out, not leaking.
Unit conversions come up constantly because vendors quote different systems. The equivalents below are for the same physical leak rate, from the conversion table in the Agilent reference:
| If the rate is 1 mbar·L/s, it is also | Value |
|---|---|
| Pascal cubic meters per second (Pa·m³/s) | 0.1 |
| Torr liters per second (Torr·L/s) | 0.750 |
| Atmosphere cubic centimeters per second (atm·cc/s) | 0.987 |
The benchmark in the tool, 1×10⁻⁶ mbar·L/s, is a typical high-vacuum figure, not a universal pass mark. Vacuum packaging lines accept rates a hundred times higher, and ultra-high-vacuum research systems need rates far lower. The equipment specification for your process always outranks a general benchmark, including this one.
What competing calculators miss
Searching for a leak rate calculator turns up three separate trades, and nearly every rival page serves exactly one of them:
- Fluid-only tools (Brave Calculator and similar): the volume-over-time division is right, but the units are whatever you typed and there is no daily-loss conversion, which is the figure that actually gets a repair approved. This page converts the worked rate into a per-day loss on every fluid run.
- Vacuum-only tools (Calculator Doc, Calculator Ultra): both print the formula with a negative sign, L = −V·ΔP/ΔT, and one works its example into a negative leak rate in liters per second, the wrong unit for the formula it shows. A leak rate is a positive gas load; this page reports it in mbar·L/s with a benchmark verdict attached.
- Pressure-decay explainers (Vac-Eng and similar guides): good engineering writing on decay testing, aimed at positive-pressure parts testing, with no working calculator and no bridge to the vacuum rate-of-rise method that uses the same three variables.
- Refrigerant compliance software (RefGuard, RefrigerantTrack and similar): the EPA math is their whole product, sold as subscriptions with service logs attached. The calculation itself is a public formula; here it is free, next to the other two modes, with the threshold verdict stated in plain language.
- The gap this page fills: all three intents in one tool, unit selectors on the fluid mode, a benchmark note on the vacuum mode, a compliance verdict on the EPA mode, and copy and share buttons so the result can go straight to a supervisor or an inspector.
Frequently asked questions
The speed at which gas or fluid escapes from a sealed system, expressed as volume per unit of time: liters per hour for fluids, mbar·L/s for vacuum systems, or an annualized percentage for refrigerant compliance.
Flow rate is intentional movement of fluid through a system; leak rate is unintended loss. They are measured for opposite reasons: one for capacity, the other for system integrity.
Leak Rate (%) = (Refrigerant Added ÷ Nameplate Full Charge) × (365 ÷ Days Since Last Addition) × 100. Full charge means the nameplate capacity, not the current fill level, and days are calendar days. Each addition event gets its own calculation.
Under 40 CFR Part 82 Subpart F the thresholds are 20% for commercial refrigeration, 30% for industrial process refrigeration and 10% for comfort cooling. Crossing one means the leak must be repaired within 30 days, or the appliance retrofitted or retired within one year. The rules apply to appliances with a full charge of 50 pounds or more under Section 608; from 2026, HFC appliances of 15 pounds or more are covered under the AIM Act rules with the same category thresholds.
This calculator treats a result at or above the threshold as crossed, so an annualized rate of exactly 20.00% on a commercial refrigeration appliance returns the repair verdict. If your number lands exactly on the line, treat it as a repair trigger and document the calculation: arguing about the last decimal place is not a compliance strategy.
Typical high-vacuum systems aim below 1×10⁻⁶ mbar·L/s, and ultra-high vacuum needs much lower rates still. Rough and medium vacuum work tolerates far higher rates. Always check your equipment specification first, because the right benchmark depends on the vacuum level the process needs.
No. The pressure-rise method measures all gas entering the chamber, and some of that gas is outgassing from walls and seals plus permeation through elastomers, not a hole. A rate that falls over repeated pump-down cycles points to outgassing; a rate that stays constant points to a real leak.
Yes, within limits. The fluid mode accepts any consistent volume and time units for gas volumes, and the vacuum mode measures gas entering an evacuated chamber. For very small gas leaks, vacuum testing quoted in mbar·L/s is the practical method, because the volumes involved are far too small to catch in a bucket.
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References
- U.S. Environmental Protection Agency. EPA2019s Refrigerant Management Program: Questions and Answers for Section 608 Certified Technicians. Accessed October 22, 2026.
- Electronic Code of Federal Regulations. 40 CFR 82.157: Appliances, Leak Repair Requirements. Accessed October 22, 2026.
- U.S. Environmental Protection Agency. Reducing Hydrofluorocarbons (HFCs) under the AIM Act. Accessed October 22, 2026.
- Agilent Technologies. Vacuum and Leak Detection Reference: Formulas, Properties, and Glossary. Accessed October 22, 2026.
- U.S. Environmental Protection Agency, WaterSense. Fix a Leak Week. Accessed October 22, 2026.
- Leybold GmbH. Vacuum Fundamentals: Leak Detection and Rate-of-Rise Testing. Accessed October 22, 2026.
- ASHRAE. Standards and Guidelines: Refrigeration and Leak Management Resources. Accessed October 22, 2026.