Nitrous Calculator
Work out what a nitrous shot really consumes, how much extra fuel it needs and how many passes your bottle holds, or rescale a jet from your kit's own chart.
A nitrous kit is sold by its "shot" in horsepower, but the numbers that matter when you run it are mass flows: how many pounds of nitrous leave the bottle each second and how much extra fuel has to go with them. This calculator turns a shot size into those flows, and it rescales a jet from the chart that came with your kit rather than inventing jet sizes from a generic formula.
How Much Nitrous a Shot Uses
Nitrous Express, one of the major kit makers, publishes a simple consumption figure: a system jetted for 100 horsepower uses about 0.8 lb of nitrous for every 10 seconds it sprays. Consumption scales with the shot, so a 200 hp shot uses about 1.6 lb in the same time.
Passes per bottle = bottle weight ÷ (lb/s × seconds per pass)
The figure holds up against first principles. A 100 hp shot at 0.08 lb/s is 288 lb of nitrous per hour. At a 6:1 ratio that brings 48 lb/hr of fuel, which works out to 0.48 lb of fuel per horsepower per hour. That is a normal brake-specific fuel consumption for a gasoline engine, so the extra fuel burned does match the extra power claimed.
| Shot | Nitrous per 10 s | Nitrous per minute | Extra fuel at 6:1 | Max passes, 10 lb bottle |
|---|---|---|---|---|
| 50 hp | 0.40 lb | 2.4 lb | 24 lb/hr | 25 |
| 75 hp | 0.60 lb | 3.6 lb | 36 lb/hr | 16 |
| 100 hp | 0.80 lb | 4.8 lb | 48 lb/hr | 12 |
| 150 hp | 1.20 lb | 7.2 lb | 72 lb/hr | 8 |
| 200 hp | 1.60 lb | 9.6 lb | 96 lb/hr | 6 |
| 250 hp | 2.00 lb | 12.0 lb | 120 lb/hr | 5 |
Treat the pass count as a ceiling. Bottle pressure falls as the bottle empties and cools, flow drops with it, and the last part of a bottle rarely delivers a full-strength pass. Most kits also only spray above a set RPM, so the real time on the button is often shorter than the pass. Weighing the bottle before and after a run is the most reliable way to learn your own consumption.
What a "100 Shot" Actually Means
The shot is the horsepower the kit is jetted to add. It is normally quoted as an engine figure, not a wheel figure, so a chassis dyno shows less than the full number after drivetrain losses. Real results vary: owners on forums such as LS1Tech have posted wheel gains close to the nominal shot, while others see noticeably less, depending on tune, nozzle placement and bottle pressure on the day.
A common drag-racing claim is that a 100 shot takes about a second off a quarter-mile pass. Our quarter-mile calculator uses ET = 6.290 × (weight ÷ HP)1/3, which gives a 3,500 lb car at 350 hp a 13.55-second estimate. Adding 100 hp brings it to 12.46 seconds, an improvement of about 1.1 seconds. Lighter or more powerful cars gain less from the same shot because ET follows a cube-root curve. Traction usually limits what you see on the timeslip.
Why Bottle Pressure Changes Everything
Nitrous is stored as a liquid with vapor above it, so bottle pressure depends almost entirely on temperature, not on how full the bottle is. Jet charts are calibrated at a specific pressure, usually 900 to 950 psi on the gauge. Below that, less nitrous flows and the engine runs rich and slow. Above it, more flows and the mixture leans out.
| Bottle temperature | Gauge pressure |
|---|---|
| 60 °F | 647 psi |
| 70 °F | 737 psi |
| 75 °F | 785 psi |
| 80 °F | 836 psi |
| 85 °F | 889 psi |
| 90 °F | 945 psi |
| 95 °F | 1,005 psi |
These are saturation pressures from the NIST Chemistry WebBook, converted from absolute to gauge pressure. They show why a bottle heater matters: a 950 psi target needs the bottle at about 90 °F, not the 85 °F that many forum tables quote. Nitrous reaches its critical point at 97.5 °F and about 1,036 psi gauge. Above that it no longer exists as a separate liquid, which makes delivery inconsistent, so heaters are set to stay below it.
Rescaling a Jet From Your Kit's Chart
Nitrous flow through a jet is proportional to the jet's area, and area grows with the square of the diameter. If your chart lists one jet for a known horsepower, the jet for a different horsepower at the same pressure is:
For example, if a chart lists a 0.040" nitrous jet for 50 hp per nozzle, 75 hp per nozzle needs 0.040 × √1.5 = 0.049". You would then pick the nearest size the chart actually lists, together with its paired fuel jet.
Some online calculators skip the chart and estimate horsepower as 70 × (jet diameter in mm)². None that we checked cites a source for the constant. At 0.040" it predicts about 72 hp, while the NOS jet map reproduced on one of those same calculator pages lists 0.040" for 50 hp per nozzle. Nozzle design, line length and solenoid size all change the real flow, so the chart for your system is the only trustworthy starting point.
The Fuel Side of a Wet Shot
Nitrous oxide is 36.35% oxygen by mass, compared with about 23.1% for air. Burning gasoline completely with nitrous takes roughly 9.4 lb of nitrous per pound of fuel. Wet kits are jetted much richer than that, commonly around 5:1 to 6:1, because the extra fuel cools the charge and protects against detonation. A dry kit adds no fuel through the nozzle. Instead the engine's own injectors supply it, usually by raising fuel pressure, so the injectors and pump must already have the spare capacity. HTP's dry jetting chart for fuel-injected four-cylinder motorcycles shows the scale: a jet rated for 34 hp calls for about 12% more fuel.
Either way the fuel system now has to supply the engine's normal demand plus the shot. Check that combined figure against your injectors with the fuel injector size calculator.
Check Any Calculator's Consumption Figure
Consumption figures vary wildly online. One nitrous calculator we checked treats a 100 hp shot as about 10 lb of nitrous per hour and promises roughly 360 passes from a 10 lb bottle. Nitrous Express's figure of 0.8 lb per 10 seconds works out to 288 lb per hour, about 29 times more, which matches the fuel arithmetic above. If a calculator promises hundreds of passes from one bottle, its consumption figure is wrong.
Shot Size, Timing and Engine Safety
How big a shot an engine tolerates depends on its pistons, rings, head gasket, fuel octane and tune far more than on displacement. HOT ROD magazine's guidance treats a 100 hp shot as safe on almost any healthy engine, with 125 to 150 hp realistic only with conservative timing and fuel. A widely used baseline from kit makers is to retard ignition timing by about 1.5 to 2 degrees for every 50 hp of nitrous, and to fit colder spark plugs. Use your kit maker's instructions as the final word, since they are written for the specific nozzle and solenoid you are running.
Nitrous adds power by adding cylinder pressure, which also adds torque. Use the wheel to crank horsepower converter to compare dyno sheets on the same basis, and the NA to boosted calculator if you are weighing nitrous against forced induction.
Frequently Asked Questions
About 0.8 lb per 10 seconds, or 4.8 lb per minute of spray, based on the figure Nitrous Express publishes. A 10 lb bottle therefore gives at most about 12 full 10-second passes, and usually fewer as pressure falls.
Shot sizes are normally treated as engine (crank) horsepower. A chassis dyno shows the gain after drivetrain losses, and real results vary with tune and bottle pressure.
Whatever your jet chart was calibrated for, usually 900 to 950 psi. On NIST data that means a bottle temperature of roughly 86 to 90 °F. Keep it below the critical point of 97.5 °F.
Multiply a known jet from your kit's chart by the square root of the horsepower ratio. A 0.040" jet rated for 50 hp becomes about 0.049" for 75 hp at the same pressure. Then use the nearest jet the chart lists.
At a 6:1 nitrous-to-fuel ratio, about 48 lb/hr per 100 hp. Your pump and fuel lines must supply that on top of the engine's normal demand.
Pressure, and with it flow, drops as the bottle cools and empties, so the last part rarely delivers a full-strength pass. Purging also uses nitrous. Weigh the bottle before and after runs to measure real consumption.