Well Specific Capacity Calculator
Solve the specific capacity equation for specific capacity, pumping rate, or drawdown — with unit conversion and a full step-by-step solution.
Pumping Rate ↑
A higher pumping rate raises specific capacity proportionally, provided drawdown is measured at the same duration — doubling Q doubles S_c for a fixed s.
Drawdown ↑
More drawdown for the same pumping rate means a less productive well or aquifer, so S_c falls — S_c and s move in opposite directions.
How to Use This Calculator
Specific capacity relates three quantities from a pumping test: the pumping rate Q, the resulting drawdown s, and the specific capacity S_c itself. Pick what you want solved, then fill in the other two.
1. Choose what to solve for
Pick S_c (from Q and s), Q (from S_c and s), or s (from S_c and Q) using the three buttons under "Solve for".
2. Enter the known values
Type into the number boxes or drag the sliders for whichever fields are still editable — the greyed-out field is the one being solved.
3. Set your units
Choose a flow unit for Q (gpm, m³/h, L/s, m³/d) and a length unit for s (ft or m). S_c's unit label updates automatically to match, e.g. gpm/ft.
4. Read the result and steps
The result card shows the solved value in engineering notation, and the step-by-step panel shows exactly how it was calculated from the formula.
5. Switch to Advanced for more depth
Advanced mode adds sensitivity to a ±1% change in the known inputs, plus a rough well-productivity rating based on the resulting S_c.
6. Copy or reset
Use "Copy result" to grab the solved value, or "Reset" to return to the default worked example.
What This Tool Offers
Built around the simple but widely used specific capacity ratio from pumping-test analysis, S_c = Q/s.
Solve any of the three variables
Rearranges the formula automatically depending on whether you know (Q, s), (S_c, s), or (S_c, Q).
Mixed-unit conversion
Independent unit selectors for pumping rate (gpm, m³/h, L/s, m³/d) and drawdown (ft, m), with S_c's compound unit label tracking both automatically.
Transparent step-by-step math
Every calculation shows the rearranged formula and the substituted numbers, not just the final answer, so it can be checked by hand.
Built-in sensitivity check
See how much the result moves for a ±1% nudge in either known input — a quick way to gauge how sensitive your estimate is to measurement error.
Well productivity rating
Advanced mode flags whether the resulting specific capacity falls in a typically low, moderate, or high productivity range for quick screening.
Sliders and numeric fields in sync
Drag a slider or type a number — both update together and immediately recalculate the result.
What Is Specific Capacity?
Specific capacity (S_c) is a simple, widely used index of well and aquifer productivity, obtained directly from a constant-rate pumping test. It expresses how much yield a well produces per unit of drawdown, giving a quick way to compare wells, screen for declining performance over time, or provide a first estimate of transmissivity before more detailed aquifer testing.
Specific Capacity Formula
The relationship is a simple direct ratio:
Rearranged for the other two variables, the same relationship gives Q = S_c × s and s = Q / S_c.
How to Calculate Specific Capacity
Select the unknown variable above, enter the two known values in your preferred units, and the calculator rearranges the formula automatically:
| Solve for | Rearranged formula |
|---|---|
| S_c | S_c = Q / s |
| Q | Q = S_c × s |
| s | s = Q / S_c |
Specific Capacity Formula Variables
| Symbol | Meaning | Typical unit |
|---|---|---|
| S_c | Specific capacity of the well (yield per unit drawdown) | gpm/ft, m³/h/m, L/s/m |
| Q | Pumping (discharge) rate during the test | gpm, m³/h, L/s, m³/d |
| s | Drawdown — drop in water level below static level | ft, m |
How Pumping Rate Affects Specific Capacity
Since the two are directly proportional at a given moment in a test, a higher pumping rate raises specific capacity proportionally as long as drawdown is compared at the same elapsed time — but in real wells, pumping harder for longer usually increases drawdown too, so measured S_c commonly declines somewhat as Q increases (well loss effects).
How Drawdown Affects Specific Capacity
Specific capacity and drawdown move in opposite directions: for a fixed pumping rate, more drawdown means the well is less efficient at converting pumping into flow, so S_c falls. Comparing S_c values from the same well over time is a common, simple way to flag well fouling, screen clogging, or declining aquifer levels.
Specific Capacity Calculation Example
S_c = 300 / 30
S_c = 10 gpm/ft
Frequently Asked Questions
It varies enormously by aquifer type. As a very rough screening guide, S_c below about 1 gpm/ft is often considered low, 1–10 gpm/ft moderate, and above 10 gpm/ft high — but always compare against wells in the same local aquifer rather than these generic bands.
Drawdown keeps growing the longer a well is pumped as the cone of depression expands, so S_c measured early in a test is usually higher than S_c measured after several hours or days at the same rate — always note the test duration alongside the value.
Yes, approximately — empirical relationships (such as those built on the Theis equation) convert S_c to an estimated transmissivity for a quick first pass, though a proper aquifer test with time-drawdown analysis gives a more reliable value.
The calculator accepts gpm, m³/h, L/s, or m³/d for pumping rate, and ft or m for drawdown. Specific capacity's unit label updates automatically to match whichever pair you select.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| Sc | Specific capacity | m3/day/m |
| Q | Pumping rate | m3/day |
| s | Drawdown | m |
What it means
Specific capacity (Sc) is the ratio of the pumping rate (Q) to the drawdown (s) in a well. It is a measure of well efficiency: a higher Sc means the well yields more water per unit of drawdown. It is used in well design and evaluation, to compare wells, and to estimate transmissivity. It is also used in aquifer tests. Understanding specific capacity helps groundwater engineers select pumping equipment, design well fields, and manage groundwater resources effectively.
Worked example
Well Specific Capacity – Two Detailed Examples
Real‑World| Parameter | Value |
|---|---|
| Pumping Rate Q (m³/day) | 500 |
| Drawdown s (m) | 5 |
| Parameter | Value |
|---|---|
| Q | 800 |
| s | 8 |
Common mistakes
- Specific capacity: Sc = Q / s – the pumping rate per unit drawdown.
- Q: Pumping rate – in m³/day or L/min.
- s: Drawdown in the well – in metres.
- Units: m³/day per metre (m²/day) or equivalent.
- Not constant: Sc decreases with pumping time and is affected by well efficiency.
Applications
Well specific capacity, Sc = Q/s, is the pumping rate per unit drawdown, providing a measure of well efficiency and aquifer productivity. This is used to evaluate well performance, to compare wells, and to estimate aquifer properties. Hydrogeologists use specific capacity data from step‑drawdown tests to determine the well loss and the formation loss components. By monitoring Sc over time, professionals can detect changes in well condition (e.g., clogging) or aquifer behaviour. This parameter is essential for well design, maintenance, and groundwater management.
- Well performance evaluation and efficiency assessment
- Comparison of well yields for water‑supply planning
- Step‑drawdown test analysis for well losses
- Monitoring of well clogging and rehabilitation needs
- Estimation of aquifer transmissivity from specific capacity
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