Two numbers, and only one of them is about pounds
Total fuel is a multiplication and it is rarely the thing that goes wrong: burn rate times hours, buy a bit more than that. The reload interval is what actually shapes the cook, because it decides how often somebody has to be standing at the firebox. A basket that holds five pounds at a pound and a half an hour is an interval of three hours and twenty minutes, which is a manageable night. The same pit running hot at three pounds an hour is a one-hour-forty interval, which is not a night anyone enjoys.
That is why the calculator puts each reload on the clock rather than just counting them. Seven reloads sounds fine written down. Seven reloads at 11:20, 1:00, 2:40, 4:20 and so on reads differently.
What moves burn rate, roughly in order
| Factor | Direction | Why it matters more than people expect |
|---|---|---|
| Pit running temperature | Strong | The fire has to make up every BTU leaving through the walls, and that loss climbs with the temperature difference |
| How well the chamber seals | Strong | Air leaking in at the door is fuel burned for nothing |
| Wind | Strong on a thin-walled pit | Convective loss off the outside of the chamber, plus it drives the draft harder than the vents intend |
| Outside temperature | Moderate | Same mechanism as the pit temperature, from the other side |
| Wood moisture | Moderate | Energy spent boiling water off is energy that never reaches the meat |
| Fuel type and brand | Smaller than the marketing suggests | Real, but usually swamped by everything above it |
Measuring your own rate takes one cook
Weigh the fuel before it goes in. Keep the reload weights, or just weigh what is left in the bag at the end. Divide the difference by the hours the pit ran. That is the whole method, and one afternoon of it is worth more than any table, because the answer belongs to your pit in your weather rather than to somebody else in a different climate.
Do it twice — once in mild weather and once in cold or windy weather — and you will have the range that matters when you are planning a cook in November. The calculator has a sensitivity block that shows what a twenty percent higher rate does to the pounds, the reload count and the bags, which is the quickest way to see whether your spare is big enough.
The failure mode worth insuring against
Running out of fuel at three in the morning is not merely inconvenient, it is the point at which a cook goes badly wrong, because a cold pit with meat in it cannot simply be restarted where it left off. A spare bag is the cheapest insurance on the whole cook. The calculator counts what actually burns and what you should carry separately, so the spare is a visible decision rather than an accident of rounding.
Questions people ask
How much charcoal does a 12-hour smoke use?
Multiply your own burn rate by twelve. At a pound and a half an hour that is eighteen pounds, which is a bag and a bit at typical bag sizes. But the rate is the whole answer and it varies by more than a factor of two between a well sealed pit in still air and a thin one in wind, so the useful move is to weigh the fuel through one cook rather than take any published figure, this page included.
How often do I need to add wood to an offset smoker?
The interval is the size of a reload divided by the burn rate. Five pounds of splits at a pound and a half an hour is three hours twenty minutes. In practice people add smaller amounts more often to keep the fire clean, which shortens the interval proportionally: two and a half pounds at the same rate is an hour forty. The calculator will put those on the clock from your lighting time so you can see how many land overnight.
Do pellets burn at a steadier rate than charcoal?
The feed is steadier, because an auger meters pellets by the turn rather than by how the fire happens to be sitting. That makes a measured pounds-per-hour figure more reliable for a pellet cooker than for a firebox fed by hand. It does not make the figure universal — it still moves with pit temperature and outside conditions, and a pellet cooker in a cold wind works considerably harder than the same one in July.
Is it safe to run a smoker on a covered porch?
Charcoal and wood produce carbon monoxide continuously while they burn and it is odourless and colourless. People are killed every year by charcoal under a roof, in garages, in sheds and in tents, including with doors and windows open. This page will not give you a clearance distance or a ventilation procedure, because that is not something a calculator can determine for your structure. Keep fires outdoors and well away from the building, and treat anything with a roof over it as indoors.
How much fuel should I keep spare?
At least one full package, and more if the cook runs overnight or the shops are closed at the hour you would need it. The sensitivity block on this page shows what a twenty percent higher burn rate does, which is a realistic amount for a cold or windy day, and comparing that to your spare is the quickest test. Unused fuel keeps indefinitely if it stays dry, so the only cost of over-buying is storage.