Bit Hydraulics
Bit-hydraulics maths — total flow area from nozzle sizes, nozzle velocity, bit pressure drop, hydraulic horsepower, HSI and jet impact force. Field and metric units, fully offline.
Open Bit Hydraulics →What is the bit hydraulics calculator?
A drilling bit-hydraulics calculator that runs entirely in your browser. From a set of nozzle sizes and a flow rate it works out the total flow area (TFA), the velocity of the mud leaving the jets, the pressure drop across the bit, the hydraulic horsepower and HSI (horsepower per square inch of bit face), and the jet impact force. Nozzle sizes are entered the way the field does it — in 32nds of an inch as a comma-separated list, so 12, 12, 12 means three 12/32-inch jets. Field units (ppg, gpm, psi, in) and metric units (SG, L/min, bar, mm) are both supported, and every result updates as you type. Nothing is uploaded; the maths uses the standard Lapeyrouse/IADC constants and a nozzle discharge coefficient of 0.95, and stays on your device.
How to use Bit Hydraulics
- Choose your units — Use the Field / Metric switch. Field is ppg, gpm, psi and inches; metric is SG, litres per minute, bar and millimetres.
- Enter the nozzles — Type the nozzle sizes in 32nds of an inch as a comma-separated list, e.g. 12, 12, 12. Blank or invalid entries are ignored.
- Add flow and mud data — Enter the flow rate, and for pressure or impact the mud weight and (for HSI) the bit diameter. Standpipe pressure is optional.
- Read the results — Each tab shows the main figure large; smaller lines give the nozzle count, Σd², or the pressure drop as a percentage of standpipe pressure.
Frequently asked questions
How do I enter nozzle sizes?
In 32nds of an inch, as whole numbers separated by commas. Three 12/32-inch nozzles are entered as 12, 12, 12. This works the same way in both field and metric modes.
Why does the pressure-drop constant look unusual?
The field bit pressure drop uses 10858, which already carries the standard nozzle discharge coefficient of 0.95. It is not the same as the 12031 used when the coefficient is applied separately.
What is HSI and why does it need the bit diameter?
HSI is hydraulic horsepower per square inch of bit face. Dividing the bit power by the bit's cross-sectional area (0.7854 × diameter²) gives a figure you can compare against a target for good hole cleaning.
Does it work offline?
Yes. There are no dependencies and no network calls, so it runs on a rig laptop with no signal, and your last inputs are saved on your device.
Tips
- Smaller total flow area gives higher nozzle velocity and more jet impact for the same flow rate, but also a larger bit pressure drop.
- Enter standpipe pressure on the Pressure & power tab to see what share of the total system pressure is being spent across the bit.
- Use true, current nozzle sizes — a plugged or washed-out jet changes the TFA and throws off velocity, pressure and impact together.