Glycerin Dosing Calculator

This Glycerin Calculator is developed based on the standard laboratory model proposed by Cheng (2008) for glycerol-water mixtures, specifically for instances when a desired concentration in mPas is required.

FastAPI + HTMX web app for computing glycerin–water dosing to reach a target viscosity.
Uses the Cheng (2008) glycerol–water viscosity model and tabulated density data spanning 15–30 °C (anchors at 15, 15.5, 20, 25 and 30 °C).

The calculator has two modes, switchable with the toggle at the top of the form.

First mode — Current volume. You have a fixed amount of solution on hand. Enter its volume, the glycerol it already contains, and your target viscosity; the calculator returns how much glycerin stock to add to reach that viscosity.

Second mode — Final volume. You want to prepare a specific batch size. Enter the desired final volume and target viscosity; the calculator returns the two volumes to combine — how much base solution and how much glycerin stock — to make exactly that much solution at the target viscosity. (Because glycerol–water mixing contracts, the two component volumes sum to slightly more than the final volume; the result is exact by mass.)

Quick start

# install uv if you don't have it
# On macOS and Linux
curl -LsSf https://astral.sh/uv/install.sh | sh

# On Windows
powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

# create venv and install deps
uv sync

# run the dev server
uv run glycerin-calculator
# → http://127.0.0.1:8000

Or directly:

uv run uvicorn glycerin_calculator.main:app --reload

Project layout

glycerin-calculator/
├── pyproject.toml
├── README.md
├── tests/
│   └── test_calculator.py
└── src/
    └── glycerin_calculator/
        ├── __init__.py
        ├── main.py          # FastAPI app + Plotly chart
        ├── physics.py       # Cheng model, density, unit conversions
        ├── density_data.py  # glycerol–water density tables (15–30 °C)
        ├── static/
        │   └── style.css
        └── templates/
            ├── index.html
            └── partials/
                └── result.html   # HTMX swap target

Running tests

uv run pytest -v

Model notes

• Viscosity: Cheng N-S (2008) Industrial & Engineering Chemistry Research.
  Valid for 0–100 % glycerol and approximately 0–100 °C.
• Density: bilinearly interpolated from tabulated literature values — piecewise-linear in concentration and linear in temperature between anchor tables at 15, 15.5, 20, 25 and 30 °C. Within that band the entered temperature is used directly; outside 15–30 °C the value is extrapolated from the nearest anchor pair, so verify the density assumption at temperature extremes.
• Stock basis: confirm whether your 86% stock is specified w/w or v/v — both options are supported via the toggle.

Changelog

See CHANGELOG.md for release history. Current version: 0.5.0.

Dependencies

Package	Role
fastapi	HTTP framework
uvicorn	ASGI server
jinja2	HTML templating
python-multipart	form parsing
plotly	server-side chart JSON