Nitrous jet sizing is fundamentally about flow area, not the horsepower number printed on the jet kit's box. This calculator walks backward from a target horsepower shot to a jet size, using the same orifice-area scaling that jet manufacturers rely on internally, then shows you the real-world jet size you'd actually buy.
How the Nitrous Jetting Calculator works
At a given bottle pressure, the mass flow rate through a jet is proportional to its cross-sectional area — which means diameter squared, not diameter itself. This calculator anchors that relationship to a commonly published wet-nitrous jetting combo: a .035" nitrous jet supporting roughly a 100 hp shot, paired with a .020" fuel jet at a 1:5.5 fuel:nitrous ratio by weight. From that anchor, it scales the ideal jet diameter for any target horsepower using the square-root-of-area relationship, then rounds to the nearest whole thousandths-of-an-inch size, since real jets are sold in fixed increments rather than continuous sizes.
Inputs and what they mean
Target HP shot is the horsepower gain you want the nitrous system to add on top of the engine's baseline output — typical street shots run 50 to 150 hp. System type determines whether a fuel jet is calculated at all: wet systems spray fuel alongside the nitrous and need a matching fuel jet, while dry systems inject nitrous only and lean on the factory fuel injectors and ECU tuning to add fuel, so there's nothing to jet on the fuel side. The target fuel:nitrous ratio (entered as 1:X) only applies to wet systems and defaults to 1:5.5, a commonly cited safe starting point — richening it (a smaller X) increases the fuel jet size, leaning it out (a larger X) decreases it.
Limits and edge cases
This calculator uses a single generic reference chart, not any specific manufacturer's jet numbers — real nitrous kits from different brands use different jet-to-flow calibrations, so treat the output as a planning reference rather than a drop-in spec for a particular kit. It also assumes a roughly constant nitrous bottle pressure; systems running unusually low bottle pressure, cold weather, or a nearly empty bottle will flow less than a fresh, warm, fully-pressurized bottle at the same jet size. Shots below 50 hp or above 150 hp trigger a caution note because they fall outside the typical street-safe range this tool is calibrated around — bigger shots need a stronger bottom end, adequate fuel supply, and ignition timing control that a simple jet calculator can't verify. For anything beyond a mild street shot, get the combination confirmed by an experienced nitrous tuner before running it.