How Long Does a Propane Tank Last? (Size Guide)
How long a propane tank lasts for grilling, broken down by BTU output and tank size, plus how to check remaining fuel, from our own tested-grill burn time data.
The Short Answer, Then the Real Math
A standard 20 lb propane tank lasts roughly 18–20 hours of grilling time on a typical 3-burner gas grill run at medium heat — but that number swings a lot based on your grill's BTU output, how many burners you actually run, and how hot you cook. This guide breaks down real burn times from our own tested grills, plus how to actually calculate the number for your specific setup instead of relying on a single generic estimate.
Quick Answer: Propane Tank Sizes and Typical Burn Time
| Tank Size | Propane Weight | Typical Use | Approx. Burn Time (3-burner grill, medium heat) |
|---|---|---|---|
| 1 lb disposable canister | ~1 lb | Tabletop/portable grills | 1–2 hours |
| 20 lb tank | ~15–16 lb usable | Standard backyard gas grill | 18–20 hours |
| 30 lb tank | ~24 lb usable | Larger grills, extended use | 28–32 hours |
| 40 lb tank | ~32 lb usable | High-BTU grills, heavy use | 38–42 hours |
If you only remember one number: a standard 20 lb tank on a typical backyard gas grill gets you roughly 18–20 hours of medium-heat cooking — call it 15–20 full cookouts before you need a refill or exchange, for most households.
Why "It Depends" Is the Honest Answer
BTU Output Is the Biggest Variable
Every burner consumes propane based on its BTU (British Thermal Unit) rating — a higher-BTU grill burns through the same size tank faster than a lower-BTU one, even cooking for the same amount of time. Our tested Weber Spirit E-325 (31,000 BTU combined) got roughly 18–20 hours from a single 20 lb tank across our four-week testing, in line with Weber's own estimate for that burner system. The higher-output Weber Genesis E-325 (39,000 BTU plus a 13,000 BTU sear burner) burned through roughly 3.5 tanks across a comparable testing period — noticeably faster per hour, simply because more BTU means more propane consumed per minute at the same burner setting.
How Many Burners You Actually Run
A 3-burner grill running on just one burner for a quick weeknight meal uses a fraction of the propane it would running all three burners wide open for a hard sear. Estimates based on total grill BTU output assume all burners running — if you typically cook with fewer burners lit, your tank will genuinely last longer than the table above suggests.
Heat Setting and Cook Style
High heat for searing burns propane meaningfully faster than a low, steady simmer for indirect cooking. A grill used mostly for quick, high-heat weeknight cooking will burn through a tank faster per session than the same grill used for longer, lower-heat cooks, even if total cook time is similar.
Real Burn Times From Our Tested Grills
| Grill | BTU Output | Tank Type | Measured Burn Time |
|---|---|---|---|
| Weber Spirit E-325 | 31,000 BTU | 20 lb tank | 18–20 hours |
| Weber Genesis E-325 | 39,000 + 13,000 sear | 20 lb tank | ~3.5 tanks over 8 cooks |
| Cuisinart Portable Propane Grill | 20,000 BTU | 20 lb tank | 15–18 hours |
| Cuisinart Petite Gourmet | 5,500 BTU | 1 lb canister | Several short cooks per canister |
| Megamaster Tabletop 1-Burner | Single burner | 1 lb canister | 1–2 hours per canister |
These numbers come from our own multi-cook testing logs, not manufacturer marketing estimates, which is why the Genesis and Spirit — both rated for similar total cooking area but different BTU output — show meaningfully different real-world propane consumption per hour.
The Math: Calculating Your Own Burn Time
The Basic Formula
Propane provides roughly 21,500 BTU of energy per pound. To estimate burn time at full burner output:
Burn time (hours) = (Tank weight in lbs × 21,500) ÷ Grill's total BTU rating
For a 20 lb tank on a 30,000 BTU grill running wide open: (20 × 21,500) ÷ 30,000 ≈ 14.3 hours at full output.
Why Real-World Numbers Run Higher
That formula assumes every burner runs at maximum the entire time, which almost never happens in practice — most cooks use partial burner settings, turn burners down after preheating, or run fewer than all burners. This is why our measured real-world burn times (18–20 hours on the Spirit E-325's 31,000 BTU system) run noticeably longer than the full-throttle math alone would suggest. Treat the formula as a conservative floor, not a precise prediction.
Usable Propane vs. Tank Weight
A "20 lb" propane tank is named for the weight of propane it's designed to hold, not the tank's total weight — the empty tank itself (the tare weight) is separate and usually stamped on the collar. Tanks are also filled to about 80% capacity by design, a safety standard that leaves room for propane to expand, so a full 20 lb tank actually holds closer to 15–16 lb of usable propane rather than a full 20 lb.
How to Check How Much Propane Is Left
The Weight Method (Most Reliable)
Check the tare weight (TW) stamped on the tank's collar — this is the empty tank's weight. Weigh the tank on a bathroom scale, subtract the tare weight, and the remainder is your actual propane weight remaining. This is the most accurate method available without a built-in gauge.
The Hot Water Method
Pour warm (not boiling) water down the side of the tank, then run your hand down the same spot. The propane inside absorbs heat from the tank wall, so the section still containing liquid propane will feel noticeably cooler to the touch than the empty section above the fill line — the boundary between warm and cool marks your approximate fuel level.
Built-In Fuel Gauges
Some premium grills include a built-in propane gauge that reads tank weight without needing to disconnect anything. Our tested Weber Genesis E-325 includes this feature, and it made a real, measurable difference across our testing — no more guessing or lifting the tank to estimate what's left, which is otherwise the most common way people get caught mid-cook with an empty tank.
Propane Tank Sizes Explained
1 lb Disposable Canisters
Used almost exclusively on tabletop and portable grills like the Megamaster Tabletop 1-Burner. Convenient and lightweight for camping or tailgating, but not economical for regular backyard use — the per-pound cost of propane in small disposable canisters runs significantly higher than refilling a standard 20 lb tank.
20 lb Tanks (Standard Backyard Size)
The default size for the overwhelming majority of full-size gas grills, including every 20 lb-tank grill in our tested lineup. Most grill carts are sized specifically around this tank, and it's the size available for exchange at most gas stations, hardware stores, and grocery stores.
30 lb and 40 lb Tanks
Larger tanks extend time between refills proportionally but are heavier, bulkier, and less universally supported by grill cart designs and exchange programs — worth considering only if you grill very frequently and want to minimize refill trips, or if you're running a higher-BTU grill that burns through a standard 20 lb tank faster than you'd like.
Tips for Making a Tank Last Longer
Turn Down Burners After Preheating
Most grills don't need full-blast heat for the entire cook — preheat on high, then dial back to your actual target temperature once food goes on. Running every burner wide open for the full cook duration is one of the most common ways to burn through a tank faster than expected.
Close the Lid
An open lid loses heat continuously, forcing burners to work harder to maintain temperature. Keeping the lid closed except when actively flipping or checking food conserves fuel meaningfully over a long cook.
Match Burner Count to What You're Cooking
Running all three burners on a 3-burner grill to cook two burgers wastes propane relative to running just one burner sized appropriately for the food on the grate. Save multi-burner operation for when you're actually using the full grate.
Frequently Asked Questions
How long does a 20 lb propane tank last on a gas grill?
Roughly 18–20 hours on a typical 3-burner grill run at medium heat, based on our own testing across multiple grills. Higher-BTU grills burn through a tank faster; lower-BTU or single-burner grills last longer.
How can I tell how much propane is left in my tank without a gauge?
Weigh the tank and subtract the tare weight (TW) stamped on the collar — the remainder is your actual propane weight. Alternatively, pour warm water down the tank's side and feel for the temperature boundary between the cool, propane-filled section and the warm, empty section above it.
How many grilling sessions does one propane tank last?
For most households cooking for about an hour per session, a 20 lb tank typically covers 15–20 cookouts before needing a refill or exchange, based on our measured burn times across several tested grills.
Does a higher BTU grill really use more propane?
Yes, meaningfully. Our tested Weber Genesis E-325 (39,000 BTU plus a 13,000 BTU sear burner) burned through roughly 3.5 tanks across the same testing period where the lower-output Weber Spirit E-325 (31,000 BTU) lasted a full tank for 18–20 hours — higher BTU output directly means faster propane consumption at comparable settings.
Is it cheaper to refill a propane tank or exchange it?
Refilling at a propane retailer is usually cheaper per pound than an exchange program, since exchange tanks are often not filled completely full and you're paying partly for the convenience and a fresh-looking tank. Refilling your own tank to capacity typically gives you more usable propane for the money.
Why does my 20 lb tank feel like it has less than 20 lbs of propane in it?
Tanks are filled to about 80% capacity by safety design, leaving room for propane to expand. A full 20 lb tank holds closer to 15–16 lb of usable propane, not a true 20 lb — this is normal and not a sign of an underfilled tank.
Final Takeaway
A standard 20 lb propane tank lasts roughly 18–20 hours on a typical backyard gas grill, but the real number depends heavily on your grill's BTU output, how many burners you run, and your cooking style — our own testing showed a real gap between a 31,000 BTU grill and a 39,000+ BTU grill on otherwise similar tanks. Check remaining fuel by weight rather than guessing, and if you frequently find yourself running out mid-cook, either step up to a 30 lb tank or look at your burner habits before assuming your grill needs a replacement tank.
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