Purpose
A Stock and Flow Diagram shows how stocks, inflows, and outflows shape a system over time. It is especially suited when growth, delays, or capacity limits determine the dynamics.
Systems Thinking Mapping tool
Stock and Flow Diagram
Shows accumulation, delay, and capacity as behaviour over time; stocks are quantities and flows are quantities per unit of time.
Stock-and-flow diagrams show accumulation, delay, and capacity as behaviour over time. Stocks are state quantities and flows are rates of change per unit of time.
How do inflows and outflows change stocks over time?
- Participants
- 1-6
- Time
- 2–6 hours for a small conceptual model; calibration and simulation are separate.
How do inflows and outflows change stocks over time?
Stocks
Define stocks and units
Name accumulated quantities, units, starting value and reference date; set the system boundary.
Flows
Add inflows and outflows
Connect each flow to a stock and express it in the stock unit per time unit.
Dynamics
Model rates and delays
Describe rules that influence rates; mark delays and causal assumptions.
Behavior
Test behavior and scenarios
Check units, edge cases and historical behavior; simulate only with transparent assumptions.
Update the work record when new evidence, changed constraints or the planned review changes an assumption.
A good fit when
Useful for queues, staffing, inventory, pipelines or resources with relevant dynamics. Not a substitute for data analysis or calibrated simulation.
Ideal for
- Capacity Planning
- Pipeline Dynamics
- Resource Problems
Not good for
- Fast story workshops
- Pure architecture communication
Outputs
Stocks with units and initial value
The overview describes accumulated quantities with units, initial values, reference dates, and a system boundary.
Conserved flows with consistent rate units
The flow overview connects each inflow and outflow to the relevant stock. Each rate uses that stock’s unit per unit of time.
Rules, parameters and delays
The model description contains traceable rules and parameters that influence rates, together with delays and causal assumptions.
Consistent model and scenario questions
The consistent model records units, edge cases, and historical behaviour and makes simulation assumptions transparent.
Stock and Flow Diagram working record
Fictional example
Method-specific prompts and a fictional worked example; template prompts remain empty.
Define stocks and units
Define each stock with unit and opening balance.
**Boundary:** Service cases from arrival to resolution.
Add inflows and outflows
Balance each stock as opening value plus inflows minus outflows.
**Stock:** Open cases, unit cases; fictional opening stock: 10 cases at the start of the week.
Model rates and delays
Write rate rules and document evidence, assumptions and delays.
**Inflows:** New cases: 8 cases/week for one week.
Test behavior and scenarios
Test plausible behavior; report calibration and limits.
**Outflows:** Resolved cases: 6 cases/week over the same week.
The guide explains stock-flow units and consistency: stocks use quantity units, flows use quantity per time and change stocks.
First step
Define the boundary, time period, stock quantities and their measurement units.
Good to do first
Deep dive
How it works
First the relevant stocks, flows, and auxiliary variables are defined. Then initial values, rates, and delays are modeled so movement over time becomes traceable. Finally the team checks how changes in parameters shift the system's behavior.
In detail
Stock and Flow Diagrams work because they make stocks, inflows and outflows, and delays explicit, capturing dynamics more precisely than in general causal pictures. Good use pays attention to a clean distinction between what accumulates and what changes it. The model becomes especially useful when it explains why a system reacts sluggishly, overshoots, or responds surprisingly strongly to small interventions.
Facilitation
First clarify which quantities accumulate over time and how their increase or decrease would be recognizable in everyday terms. The situation becomes especially revealing where a supposed influence in truth only acts indirectly through another stock. Close with a deliberately small, consistent model and the delays you want to keep observing or simulating.
The method guide walks execution through 4 phases, timing, 4 pitfalls, and clear stop criteria.
Open method guideYour perspective
Does this method help with your work?
Your feedback helps shape the next improvements to methodatlas.
Sources and topics
Artifact templates
Stock and Flow Diagram: WorksheetPlan a session or initiative to match the actual scope of work.markdown
Stock and Flow Diagram: WorksheetPlan a session or initiative to match the actual scope of work.
markdownstock-and-flow-diagram-working-template.md
Plan a session or initiative to match the actual scope of work.
Stock and Flow Diagram: Worksheet
Question
To be confirmed
Desired outcome
To be confirmed
Scope
Prepare the full method Time: 2–6 hours for a small conceptual model; calibration and simulation are separate.
Complete this worksheet on paper or in your own document during the work.
Preparation for this scope
Method setup
- Materials: Boundary, available time series, units list, domain rules and a modeling tool.
- Roles: Domain owners · system dynamics modeler · data specialist; review every quantity and assumption together.
- Advance information: Choose materials, data access and participants to fit the research or decision question.
- Overall time needed: 2–6 hours for a small conceptual model; calibration and simulation are separate.
- Setup: Open the method-specific structure. Fictional examples are for orientation only; keep the blank worksheet separate from actual findings.
Prepare for the work steps
Stocks: Define stocks and units
- Define the boundary, time period, stock quantities and their measurement units.
- Boundary, available time series, units list, domain rules and a modeling tool.
Flows: Add inflows and outflows
- Stocks with units and initial value
- Boundary, available time series, units list, domain rules and a modeling tool.
Dynamics: Model rates and delays
- Conserved flows with consistent rate units
- Boundary, available time series, units list, domain rules and a modeling tool.
Behavior: Test behavior and scenarios
- Rules, parameters and delays
- Boundary, available time series, units list, domain rules and a modeling tool.
Stock and Flow Diagram working record
Define stocks and units
Define each stock with unit and opening balance.
...
Add inflows and outflows
Balance each stock as opening value plus inflows minus outflows.
...
Model rates and delays
Write rate rules and document evidence, assumptions and delays.
...
Test behavior and scenarios
Test plausible behavior; report calibration and limits.
...
Blank worksheet contains prompts only, with no example data.
System Dynamics Learning Guide
Stocks: Define stocks and units
Expected artifact: Stocks with units and initial value
Stocks with units and initial value
Entry:
...
- Can the quantity be measured at a point in time?
Flows: Add inflows and outflows
Expected artifact: Conserved flows with consistent rate units
Conserved flows with consistent rate units
Entry:
...
- Does flow unit equal stock unit per time?
Dynamics: Model rates and delays
Expected artifact: Rules, parameters and delays
Rules, parameters and delays
Entry:
...
- Are mechanisms and units checkable?
Behavior: Test behavior and scenarios
Expected artifact: Consistent model and scenario questions
Consistent model and scenario questions
Entry:
...
- Are values, period and model limits clear?
Open questions and next steps
...
Method guide: https://methodatlas.meierhoff-systems.de/en/methods/stock-and-flow-diagram/run-sheet
Alternatives and neighbors
Fitting alternatives with decision guidance, followed by other related methods.
Systems Thinking
Causal Loop Diagram
Instead of Stock and Flow Diagram, when qualitative cause-and-effect relationships are enough and stocks don't yet need to be quantified.
Systems Thinking
System Archetypes
Moves relationships, patterns, and leverage toward a concrete result through "formulate current observations", "introduce archetype cards", and "discuss leverage and derive actions".
Systems Thinking
Behavior Over Time Graph
Traces developments over time and reveals turning points, patterns, and possible causes of a trend.
Systems Thinking
Leverage Points
Moves relationships, patterns, and leverage toward a concrete result through "introduce the twelve leverage points", "collect planned actions", and "formulate a strategy across multiple levers".
Systems Thinking
Rich Picture
Makes an unclear problem situation visible with actors, tensions, and flows before premature solutions emerge.
Systems Thinking
Futures Wheel
Arranges direct and indirect consequences of a change radially, so future impacts and cascades of consequences become visible.
Constraints and origin
HighWorkshop + async2-6 h
Profile
- Method form
- Mapping tool
- Participants
- 1-6
- Time
- 2-6 h
- Maturity
- Established
- Origin
- Systems Thinking Community
Next up: System Dynamics Simulation