Drilling Calculators
Run real drilling pressure calculations using the exact formulas taught in IWCF and IADC well control certification. Every calculator shows the formula it uses, so you can check the math by hand rather than trusting a number on a screen.
This page's free mud calculators cover the core math used industry-wide: mud weight window, hydrostatic pressure, kill mud weight, and pressure gradient — every formula shown, no signup.
Start Here: Hydrostatic Pressure
Mud weight and depth is the calculation everything else on this page builds on. Type into both boxes and it works out as you go.
That is the static column only. To check it against pore and fracture pressure and get a kick or lost-circulation warning, use the full hydrostatic pressure calculator. For the full concept — pore/fracture pressure, ECD, trip margin, MAASP — see the hydrostatic pressure reference page. Want the six core formulas in one place to check against before you open a calculator? See the drilling formulas cheat sheet.
Which Calculator Do You Need?
Most people land here mid-problem. Find your situation:
| Your situation | Use this |
|---|---|
| You need the mud column pressure at a given depth | Hydrostatic Pressure |
| The well is shut in and you have SIDPP recorded | Kill Sheet |
| A report quotes sg or kg/m³ and you work in ppg | Mud Weight Converter |
| You're planning casing points or picking a mud weight | Mud Weight Window |
| You need a ring gasket, stud, or nut size for a flange | Flange & Ring Gasket Lookup |
| You're making up a bit and need the right torque | Bit Thread & Torque Lookup |
| You need lag strokes, lag time, or pump output | Lag & Volume |
| You're tracking drilling line wear against its service life | Ton-Mile |
| Rig floor elevation changed and depths need reconciling | ODF Depth Correction |
| You need hole capacity, displacement, or a running depth tally from pipe specs | Drill Pipe Tally |
| You need to bullhead a well and check the surface-pressure limits | Bullheading |
| Shut-in pressure is climbing and you need a migration rate or bleed volume | Gas Migration |
| You need buoyed weight for closed-ended pipe or two different fluids | Buoyancy & Tubular Weight |
| You're on a subsea well and need the riser margin | Riser Margin |
| You need a safe pipe-pull length before fill-up on a trip | Wet & Dry Pipe Pull Margin |
| You're killing a directional or horizontal well and need KOP/EOB pressure checkpoints | Horizontal Kill Sheet Additions |
| You need the friction-adjusted mud weight while circulating, not just static | ECD |
| You have a fresh LOT/FIT and need today's surface-pressure limit | MAASP |
| You need to know how big a kick the shoe can take before it's at risk | Kick Tolerance |
If you're new to this and not sure which applies, start with the hydrostatic pressure calculator — every other calculation on this page builds on it.
If you would rather work it by hand, the drilling formulas cheat sheet lists the same equations with their units and constants written out.
The Calculators
Hydrostatic Pressure Calculator
Calculate hydrostatic pressure, compare against pore and fracture pressure, and get an instant safe/unsafe status.
Formula: HP = MW × 0.052 × TVD
Open Calculator →Kill Sheet Calculator
Calculate kill mud weight, formation pressure, and initial/final circulating pressure after shutting in on a kick.
Formula: KMW = OMW + (SIDPP ÷ (0.052 × TVD))
Open Calculator →Mud Weight Converter
Convert mud weight between ppg, specific gravity, lb/ft³, kg/m³ and psi/ft, plus pressure and depth. Every field updates as you type.
Formula: psi/ft = ppg × 0.052
Open Converter →Mud Weight Window Calculator
Visualize your safe drilling window between pore pressure and fracture pressure gradients at any depth.
Formula: Pore gradient < MW < Fracture gradient
Open Calculator →Flange & Ring Gasket Lookup
API 6A/6BX bore size and pressure rating to ring gasket number, stud count, stud size, and flange OD.
Standard: API 6A / 6BX
Open Lookup →Bit Thread & Make-Up Torque
Bit size to thread connection, then make-up torque for that connection on PDC and roller cone bits.
Range: Minimum / Maximum / Max. Severe
Open Lookup →Lag & Volume Calculator
Pump output, string and annular volumes, and lag strokes and lag time down to the bit and back up.
Formula: Strokes = Volume ÷ Pump Output
Open Calculator →Ton-Mile Calculator
Round trip, drilling, coring, short trip, and setting-casing ton-miles for drilling line service life.
Standard: API RP 9B / Lapeyrouse
Open Calculator →ODF Depth Correction
Reconcile drill pipe tally depth against wireline depth after a rig floor elevation change.
Formula: Final = C1 + C2
Open Calculator →Drill Pipe Tally Calculator
Hole capacity, steel displacement, and a running joint-by-joint depth tally from OD, ID, and joint count.
Formula: Capacity = ID² ÷ 1029.4
Open Calculator →Bullheading Calculator
Kill fluid weight, formation fracture pressure, initial/final max surface pressure, volume to bullhead, and pump rate vs. gas migration.
Formula: Max Surface Pressure = FFP − Hydrostatic
Open Calculator →Gas Migration Calculator
Migration rate from a shut-in pressure buildup, and the volumetric-method bleed volume to hold bottomhole pressure steady.
Formula: Rate = Pressure Increase ÷ Mud Gradient
Open Calculator →Buoyancy & Tubular Weight
Buoyed pipe weight for open-ended pipe, closed-ended pipe, and pipe carrying a different fluid inside than the annulus.
Formula: BF = 1 − (MW ÷ 65.5)
Open Calculator →Riser Margin Calculator
Mud weight margin for a subsea well if the riser column were lost and replaced by seawater.
Formula: RM = ΔHydrostatic ÷ 0.052 ÷ Interval
Open Calculator →Wet & Dry Pipe Pull Margin
How much pipe can come out of the hole, wet or dry, before hydrostatic pressure drops by a target amount.
Formula: L = (ΔP × Annulus Cap) ÷ [0.052 × MW × ...]
Open Calculator →Horizontal Kill Sheet Additions
Extra drillpipe pressure checkpoints at kick-off point and end of build for a directional or horizontal well kill.
Formula: Pressure = ICP − (ICP−FCP) × Strokes Ratio
Open Calculator →ECD Calculator
Annular velocity, annular friction pressure loss, and equivalent circulating density once pumps are on.
Formula: ECD = MW + (Annular Pressure Loss ÷ 0.052 ÷ TVD)
Open Calculator →MAASP Calculator
Maximum allowable annular surface pressure at the casing shoe from your LOT/FIT test and current mud weight.
Formula: MAASP = LOT/FIT Pressure + [(LOT/FIT MW − Current MW) × 0.052 × Shoe TVD]
Open Calculator →Kick Tolerance Calculator
The ppg-equivalent gas kick your current MAASP can absorb at the shoe, using the standard zero-gradient assumption.
Formula: KT = [MAASP − (Influx Ht × MW × 0.052)] ÷ (0.052 × TVD)
Open Calculator →MAMW & New MAASP Calculator
Maximum allowable mud weight from your LOT/FIT test, then the new MAASP once a kill mud weight is set.
Formula: MAMW = MW + [LOT/FIT ÷ (0.052 × TVD)]
Open Calculator →Trip Margin / Safety Factor
The extra mud weight carried above formation balance to protect against swabbing while tripping out.
Formula: TM/SF = MW + [Safety Margin ÷ (0.052 × TVD)]
Open Calculator →Annular Velocity Calculator
How fast fluid moves up a given annular section at a chosen pump rate — the number that decides hole cleaning.
Formula: AV = Pump Output ÷ Annular Capacity
Open Calculator →New Pump Pressure Adjustment
New circulating pressure after a stroke-rate change or a mud weight change.
Formula: P2 = P1 × (SPM2 ÷ SPM1)²
Open Calculator →Barite Required Calculator
Pounds of barite per barrel needed to weight mud up from a current weight to a heavier target weight.
Formula: lb/bbl = 1500 × (MW2 − MW1) ÷ (35.5 − MW2)
Open Calculator →Kick Influx Geometry
Influx length, true vertical height, and shut-in casing pressure from a kick volume and hole inclination.
Formula: IVH = LoIAH × cos(Inclination)
Open Calculator →Tripping Pressure Effects
Pressure drop per foot pulling dry or wet pipe, and mud level drop tripping out without topping up.
Formula: ΔP/ft = MW × 0.052 × [Steel Disp ÷ (Cap − Steel Disp)]
Open Calculator →BOP Closing & Opening Ratio
Hydraulic operating pressure needed to close or open a BOP at a given wellhead pressure and rated ratio.
Formula: Pressure Required = Wellhead Pressure ÷ Ratio
Open Calculator →Slug Volume & Pit Gain
Slug volume for a desired dry pipe length, and the expected pit gain from pumping it.
Formula: V = (Length × Capacity × MW) ÷ (Slug Wt − MW)
Open Calculator →Bit Hydraulics Calculator
Total flow area from real nozzle sizes, then jet velocity, bit hydraulic horsepower, and HSI.
Formula: Vn = 0.32 × Flow Rate ÷ TFA
Open Calculator →Drill-Off Test Worksheet
Log weight-on-bit and rotary readings and get rate of penetration for every step, live — the field method for finding optimum WOB and RPM.
Formula: ROP = Footage ÷ Time × 3600
Open Calculator →IADC Dull Bit Grading Reference
The eight-position code for grading a dull bit — cutting structure wear, dull characteristics, location, bearings/seals, gauge, and reason pulled.
Standard: IADC 8-Position System
Open Reference →IADC Rock Bit & PDC Classification
Roller cone series, sub-series and bearing codes, plus PDC body, formation, cutter, and profile codes decoded.
Standard: IADC Bit Classification
Open Reference →Horizontal Tank Capacity Calculator
Diameter and length to a full fill-height-to-volume table, plus an instant fill-height lookup, in gallons or litres.
Formula: A(h) = r²cos⁻¹((r−h)/r) − (r−h)√(2rh−h²)
Open Calculator →Units and Conventions
Every calculator on this page uses oilfield units as standard:
- Mud weight — pounds per gallon (ppg)
- Pressure — pounds per square inch (psi)
- Depth — feet, true vertical depth, not measured depth
- Gradient — psi per foot
The depth distinction matters more than anything else on this list. Hydrostatic pressure depends only on the vertical height of the fluid column, so a deviated or horizontal well can have a measured depth far greater than its TVD while the bottomhole pressure tracks TVD alone. Feeding measured depth into any of these calculators on a deviated well will overstate your pressure, sometimes badly.
Frequently Asked Questions
Where does the 0.052 constant come from?
It converts pounds per gallon into psi per foot. A column of fluid one foot tall over one square inch of area holds 12 cubic inches, which is 12 ÷ 231 = 0.05195 gallons. Multiply mud weight in ppg by that figure and you get the pressure that column exerts in psi per foot. The industry rounds it to 0.052.
Should I use TVD or measured depth?
Always true vertical depth for any pressure calculation. Measured depth is used for pipe volumes, strokes, and lag time — not hydrostatic pressure.
Can I use these during an actual well control event?
No. These are reference and training tools. Live well control decisions belong to your certified well control supervisor working from your company's approved procedures and a physical kill sheet. Use these to study, to check your understanding, or to sanity-check a number after the fact.
Do these match the IWCF and IADC exam formulas?
Yes — the formulas shown are the standard ones taught in well control certification. Working through them by hand and checking against the calculator is a reasonable way to prepare, but no website replaces an accredited course.
Do you support metric units?
Not currently. Everything runs in oilfield units (ppg, psi, ft). For SI work the equivalent hydrostatic constant is 0.0981 when using specific gravity and metres to get bar.
Is my data stored?
No. Every calculation runs client-side in your browser. Nothing is transmitted or saved.