Enter the weight of you and your bike and the width of your tires. You get a front and rear pressure from a published rule, a range from firm to supple, and a hard stop at the limit of your rims.
A pressure is only as good as the gauge that sets it. Use the same one every time, so a change you make is a change in the tire, not in the gauge.
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Stay under the lowest maximum printed on your tire and your rim.
Frank Berto measured how far 50 road tires sag under load. He pushed each tire against a scale with a hydraulic jack at seven pressures and eight loads, and plotted the pressure that makes the tire drop by 15% of its width. Tire makers he worked with, including Michelin and Continental, agreed that tire drop is the right way to match pressure to load.
His chart gives, for 200 lb of rider and bike, 136 psi on 19 mm tires, 106 psi on 23 mm, 88 psi on 25 mm, 76 psi on 28 mm, 60 psi on 32 mm and 46 psi on 37 mm. This calculator starts from those seven points, fills in the widths between them and scales them to the load on each of your wheels.
Berto called 15% a compromise. A 13% drop gives a firmer ride and a little less rolling resistance on smooth roads; 17% is more comfortable. The calculator shows both ends as your range, assuming the contact patch grows in step with the drop. That assumption is ours: Berto gave no numbers for 13% or 17%.
Berto measured tires from 19 to 37 mm. For wider gravel tires the calculator extends his curve and tells you so. It gives no figure for mountain bike tires: Berto himself said the 15% rule does not hold for them.
Your two wheels do not carry the same weight. Bicycle Quarterly's measurements put about 45% of the weight on the front wheel of a randonneur or endurance bike and 40% on a race bike. Berto put a typical rider at about 45/55 and suggested taking 10% off the front pressure and adding 10% to the rear.
That is what the calculator does, from the split you choose. Many calculators put the front only 2% to 10% below the rear. We follow the load, so on a race bike the front comes out about a third lower than the rear, because it carries a third less weight.
The width on the sidewall is measured on a reference rim at maximum pressure. On a wider rim the same tire comes out wider. Continental puts it at 0.4 mm of tire width for every millimetre of rim: its 28 mm Grand Prix 5000 S TR measures 26.4 mm on a 15 mm rim and 29.6 mm on a 23 mm rim.
Pressure depends on the real width, so if you can, measure your tire mounted and inflated with a caliper and enter it. The printed width still counts for one thing: the hookless limit below is set by it.
Rims without hooks rely on the tire bead alone, so the ISO standard for bicycle tires sets a maximum pressure for them that falls as the tire gets wider: 550 kPa (79 psi) for tires up to 24 mm, 500 kPa (72 psi) for 25 to 29 mm, 450 kPa (65 psi) for 30 to 34 mm, 400 kPa (58 psi) for 35 to 39 mm, 350 kPa (50 psi) for 40 to 44 mm and 300 kPa (43 psi) for 45 to 54 mm.
It is not one limit of 5 bar for every tire: a 40 mm gravel tire on a hookless rim stops at 3.5 bar. Tire and rim makers add their own maximums, and the rule they all give is the same: follow the lowest. The calculator applies whichever is lowest and tells you when it has cut your pressure.
On a smooth floor, higher pressure always rolls faster: in an indoor test on a level floor, Grappe and colleagues measured 62% less rolling resistance at 1200 kPa than at 150 kPa. Real roads are not smooth. Jan Heine found supple 25 mm tires as fast at 70 psi as at 130 psi, and Silca, testing one rider on a repaved road, found losses rising much faster above the best pressure than below it: better a few psi under than a few psi over. On rough roads and gravel, lean to the supple end of your range; on smooth tarmac, to the firm end.
For rain, the usual rule of thumb is 10% less pressure for more grip. It is a rule of thumb: no study we could find measured it. The calculator applies it only if you tick wet roads.
We gave the most used tire pressure calculators the same rider on 28 September 2026: 83 kg of rider and bike, 28 mm tires, smooth road. Their answers ran from 57 to 83 psi, a spread of about 45%. None of them publishes its model, so there is no way to tell which assumption causes the difference.
This calculator publishes all of it: the tire drop data it starts from, how it scales with load, and each limit it applies. If you disagree with an assumption, you can see which one.
Berto measured road tires and said the 15% rule does not apply to mountain bike tires, whose knobs and rim widths change how they sag. Above 50 mm the calculator gives no figure.
Other calculators take 0% to 4% off for tubeless, with no study behind the number. We found none either, so tubes and tubeless get the same pressure here.
A supple race tire and a stiff puncture-resistant one sag differently at the same pressure. Berto's data is an average of the tires he tested; treat the range as the place to start and adjust by feel.
It depends on your weight and your tire width. For 200 lb of rider and bike on 28 mm tires, Berto's tire drop rule gives 76 psi in both tires, or about 68 psi front and 84 psi rear with the usual 45/55 weight split. Enter your own weight and width above.
Yes. The front wheel carries about 40% to 45% of the weight, so it needs less pressure for the same tire drop: about 10% less than the average on an endurance bike and 20% less on a race bike.
It depends on the tire width. The ISO standard sets 79 psi (550 kPa) for tires up to 24 mm, 72 psi (500 kPa) for 25 to 29 mm, 65 psi for 30 to 34 mm, 58 psi for 35 to 39 mm, 50 psi for 40 to 44 mm and 43 psi for 45 to 54 mm. Your tire or rim may set a lower maximum: follow the lowest.
Calculators take off between 0% and 4% for tubeless, but we found no study that measured it. This calculator gives the same pressure for tubes and tubeless.
The common rule of thumb is about 10% less for more grip. No study we found measured it, so treat it as a starting point.
On a perfectly smooth floor, yes. On real roads, only up to a point: above it the bike starts to bounce over the surface and you lose more than you gain.
Each uses its own model, and most do not publish it. Given the same rider on 28 mm tires, the most used ones answered anywhere from 57 to 83 psi. This one is built on Berto's published measurements and shows every step.
