Sankey Diagram Builder

What this tool actually does

It parses a list of flows, adds them up at each node, and draws the result. Nothing on the page knows what is flowing, what the nodes are, or where your numbers came from.

• The balance is addition and one comparison. A node balances when its inflow and outflow agree within the tolerance you set, as a share of the larger of the two. Loosen the tolerance far enough and anything balances.
• Inputs and outputs are inferred from the list. A node with nothing entering it is treated as a system input and a node with nothing leaving it as a system output. A stream you forgot to enter turns an internal node into a boundary and can make a wrong balance close.
• Amounts with separators are coerced. A single comma is read as a decimal point, so 1,5 is 1.5 and 1,234 is 1.234, not 1234. Each one is listed under "Check these". If the reading is wrong, the diagram is wrong by that factor and looks no different.
• A recycle is chosen by typing order. The flow whose line closes a loop is the one drawn as the return. That is a drawing decision. It changes no number.

Not checked, at all

• Units. Every amount is taken to be in the same unit on the same basis. Mixing kg/h with t/d, or mass with moles, volume or energy, produces a diagram that draws cleanly and means nothing.
• Volumes and moles are not conserved. A volumetric balance across a temperature, pressure or phase change does not close, and a molar balance across a reaction does not close, however good the measurements are.
• Components. A total balance can close while a component balance is badly wrong. Water in equals water out is a different check from mass in equals mass out.
• Accumulation. The check assumes steady state. A tank filling, a bed loading or a batch in progress shows up as missing outflow.
• Measurement uncertainty. No error bars, no data reconciliation, no weighting by meter quality. A gap smaller than your instruments can resolve is reported the same way as a real loss.
• Energy terms. For an energy diagram, nothing here knows about heat of reaction, reference states, shaft work or ambient loss unless you enter each one as a flow.
• Whether the boundary is right. The tool balances the system you drew, not the one that exists.

A diagram that closes tells you the numbers you entered are consistent with each other. It does not tell you that any of them is correct, and two wrong numbers can close a balance as neatly as two right ones.

What the picture can mislead about

• Thin flows. A flow under one pixel wide is drawn as a dashed line and is not to scale. Small does not mean unimportant: a trace stream can be the one that matters.
• Colour. The palette has eight colours and repeats after that. Two nodes sharing a colour are not related. Read the labels.
• Position and length. Only ribbon width carries a quantity. Ribbon length, node order, crossings and the height of a column mean nothing, and a node you have dragged can make a ribbon run backwards.
• Exports. A PNG carries the page font for Latin text only; other scripts fall back to your system font, and an SVG uses whatever fonts the program opening it has, so labels can sit slightly differently from the screen. Check an export before it goes into a report.

Never use this for

• Custody transfer, fiscal metering, allocation, invoicing, or any balance that money changes hands on.
• Emissions, discharge, waste or greenhouse-gas reporting to a regulator, a permit, or an auditor.
• Material accountancy for controlled, hazardous, radioactive or safeguarded substances.
• Relief, flare, vent or containment loads, or any process-safety figure taken from a balance.
• Equipment sizing or a design basis without an independent balance behind it.
• Financial statements, audits, tax, or any figure a third party will rely on.

Projects are stored in this browser only

Up to ten projects are kept in this browser's local storage, on this device, and are never sent anywhere. Clearing site data, using a private window, or switching browser or device loses them. It is a convenience, not a backup: use Export file to keep a copy of anything that matters.

Before you rely on a diagram

Trace every amount back to its source. Confirm that all of them share one unit and one basis. Rebuild the balance independently, in a spreadsheet or a process simulator, and have someone qualified in the process review it before the diagram supports a decision, a report or a design.