Work / 01 · Web tool
A soap calculator people can trust with lye
A free lye calculator for Island Enchantments, built into their Shopify store. It works out the lye and water for cold process, hot process and liquid soap, and shows how the bar will turn out, as you type.
- Client
- Island Enchantments
- Year
- 2026
- Type
- Web tool
The brief
Island Enchantments makes handmade soap and teaches soapmaking. They wanted a calculator for their customers that was free, needed no sign-up, and was accurate enough to trust with sodium hydroxide, a chemical that burns.
It had to live on their own site, inside their Shopify theme, and feel like part of the brand rather than a tool bolted on.
The approach
- Accuracy before features
Each oil has its own saponification (SAP) value. The calculator uses it with the standard 1.403 ratio between potassium and sodium hydroxide, then applies superfat and lye purity. I checked the results against published worked examples and hand calculations.
- One screen, five steps
Oils, lye and superfat, water, fragrance, additives. The weigh-out stays in view and updates on every keystroke.
- Built for the phone in the workshop
On a phone, a bar pinned to the bottom of the screen keeps the lye and water amounts visible while you scroll.
- Safety where you read it
Lye warnings sit right next to the weigh-out, where you look before you pour, not in a footnote.
The numbers stay with you
Most people use a soap calculator at the workbench, phone in one hand. The summary bar keeps sodium hydroxide and water on screen while you work down the recipe, and one tap opens the full weigh-out.
What I built
- Lye and water for cold process, hot process (including superfat oil added after the cook), liquid soap with paste dilution, and cream soap made with both lyes
- 149 oils, butters and fats, plus your own oils from a supplier's SAP value
- Nine classic starter recipes, from Castile to a shampoo bar
- Oils by percent or by weight, in grams, kilograms, ounces or pounds
- Bar qualities against the usual target ranges, with the full fatty acid profile
- Water set by lye concentration, water-to-lye ratio or percent of oils, with milks, aloe, beer and tea as liquids
- Fragrance blends checked against the IFRA Category 9 maximum from the supplier's certificate
- Additives, including the extra lye that citric acid uses up
- Masterbatch lye solutions, sizing to a mould or a number of bars, and cost per bar
- Recipes saved in the browser, share links, copy as text and a printable recipe card
- A plain-language guide: how to use it, how the numbers are worked out, and soapmaking terms
- Oil data from the public-domain Soapee data set, credited on the page
