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How long will it take to fill your tire?
Updated
Enter your tire size, the pressure now, your target, and the airflow from the listing. You get an estimate in minutes for one tire and for four. I built it because "150 PSI" tells you nothing about the wait, and airflow in L/min means little until it is turned into time.
How many minutes will it take?
This is an estimate, not a measurement. My assumptions: the air space is 80% of the simple ring shape your tire size describes. A pump delivers 60% of its stated free-flow airflow at 0 PSI, and loses 0.5 points for each PSI of average tire pressure, never dropping below 10%. Pocket pumps get a further cut to 45% of that. Cold weather, a weak battery, a long hose or a low car battery all make it slower. If the maker gives a real time for a named tire, trust that over this. Always fill to your door-jamb label and never past the tire sidewall maximum.
How the estimate works
- Air space. Your tire size gives an outer diameter, a rim diameter and a width. That ring shape, times 0.8, is my estimate of the air space. A 235/65R17 comes out at about 53 liters.
- Air needed. Going up 7 PSI means adding 7 divided by 14.7 of that volume in outside air. For the SUV tire, 28 to 35 PSI takes about 25 liters.
- Real airflow. The airflow on a listing is free flow, measured with nothing pushing back. Pushing against 30 PSI is much harder. My rule of thumb gives a pump 44% of its stated airflow over a 28 to 35 PSI top-up.
- Minutes. Air needed, divided by real airflow.
How it compares with maker claims
I checked the model against the times makers print on their own listings.
| Unit and claim on the listing | Maker says | My estimate |
|---|---|---|
| AstroAI AIRUN H, 35 L/min, 195/65R15 from 30 to 36 PSI | Under 1 minute, ideal conditions | 0.8 min |
| ETENWOLF Vortex S6, 42 L/min, 245/70R17 from 30 to 35 PSI | 1 minute | 1.2 min |
| Airmoto, 20 L/min, standard car tire from 28 to 35 PSI, pocket pump setting | About 3 to 5 minutes | 3.8 min on a 195/65R15 |
So it lands close to the makers' numbers for 12V and large cordless units. Without the pocket pump setting it would be far too kind to the Airmoto, at 1.7 minutes. Small pumps lose more of their airflow under pressure. That setting is tuned to this one maker claim, so treat it as rough.
Top-up times for common tires
All from 28 to 35 PSI, one tire, same math as the calculator.
| Tire | 20 L/min pocket pump | 35 L/min 12V unit | 42 L/min unit |
|---|---|---|---|
| Compact car, 195/65R15 | 3.8 | 1.0 | 0.8 |
| Midsize SUV, 235/65R17 | 6.3 | 1.6 | 1.4 |
| Full-size truck, 275/65R18 | 9.4 | 2.4 | 2.0 |
From flat is a different job
A top-up adds a few liters. A fill from 0 adds the whole tire. The same 35 L/min unit that tops up the SUV tire in 1.6 minutes needs about 7.0 minutes to take it from 0 to 35 PSI. On the full-size truck tire that is about 10.4 minutes. That is where duty cycle starts to matter.
A tire that went flat has a leak or damage. An inflator gets you moving only if the tire still holds air. If it has been driven on flat, or the sidewall is cut or bulged, do not reinflate it and drive. Use the spare or call for help.
All six inflators are compared on the shortlist.