# Drilling Hydraulics Formulas

> A drilling hydraulics formula guide for ECD, annular pressure loss, annular velocity, pump output, and pressure-window checks.

## Key Takeaways
- ECD adds circulating annular pressure loss to static mud density at the depth being checked.
- The same mud system can be safe statically and exceed the margin dynamically while circulating.
- Annular velocity and pump output are screening checks; hole cleaning still depends on inclination, rheology, cuttings loading, and operating limits.

## Workflow
1. Calculate static hydrostatic pressure from mud weight and TVD.
2. Estimate or enter annular pressure loss at the planned flow rate and geometry.
3. Convert annular pressure loss into ECD at the depth of interest.
4. Use annular velocity and pump-output calculators as supporting checks, not as a substitute for a full hydraulics model.

## Calculators
- [ECD calculator](/calculators/equivalent-circulating-density)
- [Annular velocity calculator](/calculators/annular-velocity-from-pump-output)
- [Triplex pump output calculator](/calculators/triplex-pump-output-per-stroke)
- [Hydrostatic pressure calculator](/calculators/hydrostatic-pressure-from-mud-weight)

## Formula References
- [Equivalent Circulating Density calculator](/calculators/equivalent-circulating-density)
- [Equivalent Circulating Density formula and calculator](/calculators/equivalent-circulating-density#formula-reference)
- [Annular Velocity from Pump Output calculator](/calculators/annular-velocity-from-pump-output)
- [Annular Velocity from Pump Output formula and calculator](/calculators/annular-velocity-from-pump-output#formula-reference)
- [Triplex Pump Output per Stroke calculator](/calculators/triplex-pump-output-per-stroke)
- [Triplex Pump Output per Stroke formula and calculator](/calculators/triplex-pump-output-per-stroke#formula-reference)
- [Hydrostatic Pressure from Mud Weight calculator](/calculators/hydrostatic-pressure-from-mud-weight)
- [Hydrostatic Pressure from Mud Weight formula and calculator](/calculators/hydrostatic-pressure-from-mud-weight#formula-reference)

## Verified Sources
- [Equivalent circulating density](https://glossary.slb.com/terms/e/equivalent_circulating_density) - SLB Energy Glossary
- [Hydrostatic pressure](https://glossary.slb.com/terms/h/hydrostatic_pressure) - SLB Energy Glossary

Important use note: calculator outputs support engineering checks, study, and review. They do not replace professional engineering judgment, company procedures, regulatory requirements, or source standards.