What is the water table?

The water table is the upper boundary of the saturated zone in unconfined aquifers — the depth below ground surface where soil and rock pores are fully saturated with groundwater. It fluctuates seasonally and in response to pumping.

What is static water level?

Static water level (SWL) is the standing-water level measured when the well is not being pumped. Record the exact measuring point, date, time and pumping status so repeated measurements remain comparable.

What is hydraulic head?

Hydraulic head is the elevation of the water surface in a well relative to a common datum (usually mean sea level). It equals land surface elevation minus depth to water when measuring a water-table aquifer.

How accurate is this calculator?

Arithmetic does not determine field accuracy. The result inherits measuring-point, survey-datum, instrument, well-construction, pumping and temporal uncertainty. Do not infer a site-wide water table from one well without hydrogeologic review.

What units should I use?

Every method accepts either feet or meters (air-line gauges in psi, kPa, or feet or meters of water). Changing units converts the values already entered, and results are always shown in both units.

What is the hydraulic gradient method?

This page performs straight-line interpolation of hydraulic head between two wells, then subtracts that head from land elevation at the point. It is only an interpolation between the entered wells—not a groundwater-flow model.

Does a well level always equal the water table?

No. In an unconfined aquifer, standing level can represent the water table. In a confined aquifer it represents the potentiometric surface, which may be above the aquifer and can even be above land surface.

Can I find my water table depth by ZIP code or address?

No calculator can accurately determine a current static water-table depth from a ZIP code or address alone. Levels fluctuate seasonally and vary across local terrain, geology, perched zones and pumping cones. For local records, consult USGS monitoring networks, state well-completion reports or the USDA NRCS Web Soil Survey, then verify with a suitable shallow well measurement.

How do I calculate depth to water from well depth and water-column height?

Subtract standing water-column height from total well depth, then subtract casing stickup when both depths are referenced to the casing top. For example: 150 ft total depth − 40 ft water column − 2 ft stickup = 108 ft below land surface. Confirm that both measurements use the same well-bottom reference.

How do I measure well water level with a steel tape?

Chalk the bottom few feet of a graduated steel tape, lower it until a whole-foot mark is at the measuring point and record that HOLD value, then pull it up and read the wet line (the CUT). Depth to water below the measuring point = hold − cut. Example: hold 60.00 ft, cut 3.42 ft gives 56.58 ft; subtract a 1.5 ft casing stickup for 55.08 ft below land surface. This is USGS procedure GWPD 1 and is accurate to about 0.01 ft.

How do I convert an air-line gauge reading to water level?

Multiply the gauge pressure in psi by 2.307 to get the feet of water above the bottom of the air line, then subtract that from the line length. A 150 ft air line reading 26 psi has about 60 ft of submerged line, so the water level is about 90 ft below the measuring point. Air-line readings are usually good only to about the nearest foot, and the line length must be known exactly.

How many gallons of water are in my well?

Multiply the water-column height by the gallons per foot of casing, which is 0.0408 × (inside diameter in inches)². A 6 inch casing holds 1.47 gal per foot, so a 200 ft well with water at 90 ft has 110 ft of water and about 162 gallons (612 L). Sampling protocols often purge three well volumes, here about 485 gallons.

Is there a depth to water table map?

This page has no map. It calculates depth from your own well measurements. For mapped or monitored levels in the US, look at the USGS National Water Dashboard and groundwater-level data or your state's well database. Elsewhere, check the national geological survey or groundwater agency. Maps show regional trends, so confirm the level at your site with a well measurement.

Water Table Depth & Static Well Level Calculator

Calculate depth to standing water from a well measuring point (electric tape, steel-tape hold and cut, or air-line gauge), or subtract hydraulic head from land-surface elevation, then see how many gallons stand in the casing. A well in a confined aquifer measures potentiometric level, not necessarily the water table.

Depth to water = the reading from the top of the well casing minus the casing stickup above ground, or land-surface elevation minus the water-level elevation (hydraulic head).

Inputs

Measurement Units

Calculation Method

Top of Casing Elevation above Ground (ft)

Height of casing top above ground surface. Enter 0 if flush with ground.

Static Water Level — depth from casing top (ft)

Enter your measurements and click Calculate.

Water Standing in the Well

Depth to water fills in from the calculator above. Lengths use the unit selected above.

Casing Inside Diameter

Total Well Depth below Ground (ft)

Depth to Water below Ground (ft)

Well Volumes to Purge

Water column: —
Casing capacity: —
Water in well: —
Purge volume: —

Field Methods, Formulas & Worked Examples

Method	Depth below land surface	Worked example
Electric tape (e-tape, sounder)	reading − stickup	27.5 − 2.5 = 25.0 ft
Steel tape (USGS GWPD 1)	hold − cut − stickup	60.00 − 3.42 − 1.50 = 55.08 ft
Air line (USGS GWPD 13)	line length − psi × 2.307 − stickup	150 − 26 × 2.307 − 1 = 89.0 ft
Pressure transducer / sounder	well depth − water column − stickup	150 − 40 − 2 = 108 ft
Surveyed elevations	land elevation − hydraulic head	820 − 795 = 25 ft

Air line: the gauge shows the pressure needed to push air out of the bottom of the tube, which equals the height of water above the tube's end. Fresh water exerts 0.4335 psi per foot, so 1 psi = 2.307 ft (0.703 m) and 1 kPa = 0.102 m. Gauge readings are typically good only to about 1 ft.

Steel tape: chalk the last few feet, lower until a whole-foot mark sits at the measuring point (the hold), pull up and read the wet line (the cut). Repeat until two readings agree within 0.01 ft. Hold − cut is the depth below the measuring point.

Water volume per foot of well casing

Inside diameter	US gal per ft	Litres per m	Gal per 100 ft
1 in (2.5 cm)	0.041	0.51	4.1
2 in (5.1 cm)	0.163	2.03	16.3
4 in (10.2 cm)	0.653	8.11	65.3
5 in (12.7 cm)	1.020	12.67	102.0
6 in (15.2 cm)	1.469	18.24	146.9
8 in (20.3 cm)	2.611	32.43	261.1
10 in (25.4 cm)	4.080	50.67	408.0
12 in (30.5 cm)	5.875	72.97	587.5

Gallons per foot = 0.0408 × (inside diameter in inches)². Example: 110 ft of water in a 6 in casing = 110 × 1.469 = 161.6 gal (611.6 L).

Reference and field limitation

Privacy: calculations run locally in your browser. The measurements you enter are not uploaded by this tool.

A consistent well measuring point is essential for comparable observations. See the USGS groundwater sampling protocol. For public monitoring wells and historical measurements, start with the USGS local water-table guidance and the USDA NRCS Web Soil Survey; neither replaces a current site measurement. USGS also distinguishes an unconfined water table from the potentiometric level observed in a confined aquifer; see its confined versus unconfined aquifer explanation. Steel-tape and air-line steps follow the USGS Groundwater Technical Procedures (TM 1-A1, GWPD 1 and GWPD 13).

Quick answer

Depth to water = the reading from the top of the well casing minus the casing stickup above ground, or land-surface elevation minus the water-level elevation (hydraulic head). With a chalked steel tape it is hold − cut; with an air line it is line length − gauge psi × 2.307. In an unconfined aquifer, that depth is the water table.

Examples

Method	Formula	Example
Electric tape	Reading − stickup	27.5 − 2.5 = 25.0 ft
Steel tape	Hold − cut − stickup	60.00 − 3.42 − 1.5 = 55.08 ft
Air line	Length − psi × 2.307 − stickup	150 − 26 × 2.307 − 1 = 89.0 ft
Elevation	Land − head	820 − 795 = 25 ft
Sensor	Depth − column − stickup	150 − 40 − 2 = 108 ft

Pick one of six methods and enter your well readings to get depth in feet and meters, then the gallons standing in the well.

Summary

This calculator converts a static well measurement to depth below land surface: an electric-tape reading, a steel-tape hold and cut (USGS GWPD 1 method), an air-line gauge pressure (GWPD 13 method), or total well depth minus water-column height. It can also subtract hydraulic head from land-surface elevation or interpolate head between two wells. Results are in feet and metres, and a well-volume panel turns the water column and casing diameter into gallons and litres. A result represents the water table only when the well is screened in the relevant unconfined aquifer; in a confined aquifer it represents potentiometric level.

How it works

Select the calculation method that matches your measurement: electric tape, steel tape, air line, well depth and water column, elevation, or two-well gradient.
Enter the readings and the measuring-point (casing stickup) height above land surface.
Click "Calculate" to get depth to water below the measuring point and below land surface, in feet and meters.
For an air line, the gauge pressure is converted to feet of water (2.307 ft per psi) and subtracted from the line length.
Enter the casing inside diameter and total well depth to see the gallons or litres standing in the well and a purge volume.

Use cases

Converting a measured static well level from casing top to depth below land surface.
Environmental site assessments requiring water table mapping.
Agricultural planning for irrigation and drainage design.
Screening field measurements before professional site evaluation.
Hydrogeology coursework and field data analysis.
Monitoring seasonal fluctuations in groundwater levels.
Comparing pre- and post-pumping static water levels.
Quick field checks during well installation or rehabilitation.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu