Trace: Soap & Lye Calculator

Free to use. The lye calculator and all six quality numbers are free forever — no account, no ads, no network, works fully offline. Trace Pro is an optional one-time purchase.

Trace is a cold-process soap calculator with cited chemistry. Every quality bound, every additive limit, every fragrance cap names its source.

FREE FOREVER
• 31 oils with SAP values for NaOH (bar soap) and KOH (liquid soap), cross-checked against AOCS official methods and USDA Agricultural Handbook 8
• Dual-lye blends for cream soap and shaving soap
• Three water expressions that interconvert cleanly: water % of oils, lye concentration %, water:lye ratio
• Superfat / lye-discount slider
• Citric acid auto-offsets the NaOH calculation (0.624 g NaOH per g citric acid, per Lovin' Soap Studio)
• Sodium lactate, ROE and salt brine math with cited ranges
• IFRA Category 9 (rinse-off toilet soap) fragrance caps for 20 common essential oils
• All six soap qualities — hardness, cleansing, conditioning, bubbly lather, creamy lather, longevity — computed from weighted-average fatty-acid composition, each shown with the range its source publishes
• Adjustable lye purity for NaOH (default 99%) and KOH (default 90%)
• Every cited source listed in one Sources screen

THE WEDGE
Most soap calculators surface "soap qualities" as opaque numbers. Trace shows the same numbers, free — but on every bound, tap to see exactly which named source backs it. Hardness 29–54: per Kevin Dunn, Scientific Soapmaking (Hampden-Sydney College, 2010). Citric acid 0.624× extra NaOH: per Lovin' Soap Studio. IFRA Cat 9 fragrance caps: per the IFRA Standards 51st Amendment (2025).

TRACE PRO — OPTIONAL, ONE-TIME
Try Pro free for 7 days of actual use — days you don't open Trace don't count against it. After that Pro is a single purchase. No subscription, ever.
• Cost per bar — price your oils once and Trace costs every batch: oils, lye and fragrance totalled, then divided by your bar weight. The one thing a free web calculator cannot do, because it never knows what you paid.
• Save & reopen recipes — keep every recipe you calculate
• Multi-batch cure tracker — log every batch from mix to cured: gel check, unmold, zap test, pH test
• Brand-aware oil-supplier presets: Bramble Berry, Soaper's Choice, Bulk Apothecary, Essential Depot, Wholesale Supplies Plus, plus Costco / Trader Joe's / Spectrum generics

SOURCES
Kevin Dunn (Scientific Soapmaking), AOCS, USDA Handbook 8, Susan Miller Cavitch (The Soapmaker's Companion), Anne L. Watson (Smart Soapmaking), Modern Soapmaking (Kenna Cote), Lovin' Soap Studio (Amanda Gail Aaron), IFRA Standards, Handcrafted Soap & Cosmetic Guild.

THE MOON DOG PROMISE
• No subscription. No ads. No account, no login, no signup, no network.
• Works fully offline. No data collection.

DISCLAIMER
Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are corrosive and can cause serious burns or eye damage. Always follow your supplier's Material Safety Data Sheet (MSDS) and the safety practices recommended by the Handcrafted Soap & Cosmetic Guild (HSCG). Trace cites named sources but does not generate recipes — independent verification against your supplier's specifications is your responsibility.

© 2026 Roman Kopaliani