Hydrostatic pressure calculator
Mud weight times true vertical depth — worked with the constant the gallon and the foot actually give, and shown against the 0.052 everybody uses, which is exactly one part in a thousand high. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
This is arithmetic, not well control. Every figure here comes from a published definition and can be checked, and none of it accounts for temperature, compressibility, cuttings loading, gas cut or anything else a real well does. Pressure and hydraulics decisions belong to a drilling engineer with the well's own data.
0.052 is not the constant. It is 0.1% high.
Every mud engineer alive uses
psi = 0.052 × pounds per gallon × feet
and 0.052 is a rounding. The real constant comes straight out of the definitions: there are 1728 cubic inches in a cubic foot and 231 in a US gallon, so a cubic foot is 1728 ÷ 231 = 7.480519… gallons; and there are 144 square inches in a square foot. So
(1728 ÷ 231) ÷ 144 = 0.051948051948…
which recurs, and therefore has no exact decimal form — any printed version of it is rounded somewhere. What is exact is how wrong 0.052 is: 0.052 ÷ 0.051948051948… = 1.001 exactly. The rule of thumb is exactly 0.1% high, at every mud weight and every depth, and always in the direction of over-reporting the pressure.
At 16 ppg and 15,000 ft that is 12.47 psi. Small. Consistent. Never in your favour if what you are watching for is a kick, and always in your favour if what you are watching for is losses — which is worth knowing in which direction, even if it has never been worth changing the habit.
True vertical depth. Not along the hole.
Hydrostatic pressure depends on the height of the column, not its length. A well that runs 20,000 ft along the hole to reach 12,000 ft below the rig floor has the hydrostatic pressure of a 12,000 ft column. Put measured depth into this box and the answer will be far too high.
In a deviated or horizontal well the two are wildly different, and it is the single easiest way to get this arithmetic badly wrong rather than slightly wrong.
Equivalent circulating density
The formation does not see the static column while the pumps are running — it sees that plus the pressure it takes to push mud up the annulus. Expressed back as a mud weight, that is the equivalent circulating density, and it is what the formation actually feels.
Put an annular pressure loss into the optional box and this page will convert it. It will not calculate it — annular pressure loss depends on the mud's rheology, the hole geometry, the flow rate and the cuttings loading, and that is a hydraulics model, not a line of arithmetic.
What this is not
This is a static column of one uniform fluid. A real well is not that. There is no temperature or compressibility correction here, no cuttings loading, no gas cut, no accounting for the mud being a different weight at the bottom than at the top, and no pore or fracture pressure to compare against.
Well control is a drilling engineer's job with a drilling engineer's software and a drilling engineer's responsibility. This page is arithmetic you can check, not a substitute for any of that.
A barrel, throughout, is exactly 42 US gallons.