What this calculator does
This tool tells you exactly how much pure water to add to a salt-water (saline) solution to dilute it from a known concentration down to a lower target concentration. It also reports the dissolved salt mass and the total mass of the final solution. The math is pure concentration arithmetic — conservation of solute mass under dilution — so it works for any solute/solvent pair expressed as a mass percent, not just table salt in water.
How to use it
Enter three values: the mass of your starting solution A (in grams), its salt concentration as a mass percent, and the target concentration you want the final solution C to have. Because adding pure water can only lower concentration, the target must be smaller than the starting concentration. Press calculate and you get the amount of water to add.
The formula explained
The key insight is that adding pure water adds no salt, so the salt mass is conserved. First find the salt: salt = mass × (concentration / 100). The final solution must contain that same salt at the new fraction, so its total mass is final = salt / (target / 100). The water to add is simply the difference: water = final - starting mass.
Worked example
Start with 200 g of 30% saline and dilute to 20%. Salt = 200 × 0.30 = 60 g. Final mass = 60 / 0.20 = 300 g. Water to add = 300 - 200 = 100 g.
So adding 100 g of water turns 200 g of 30% saline into 300 g of 20% saline.
使用注意事項與精準校對原則（6 大核心守則）
📐 1. 嚴格對齊輸入量綱與單位
輸入各項數值時請務必確認量綱（例如小時、天數、金額、百分比），避免單位不匹配引發推算偏差。
🔒 2. 純前端本機毫秒級隱私保障
所有計算邏輯 100% 在您的終端瀏覽器內完成，資料絕不上傳伺服器，嚴格守護商業與個人隱私。
📊 3. 符合公認學術與產業計算模型
演算法嚴格遵循國際通用數學公式與標準計算模型，經多重情境交叉核對，數值嚴密精確。
📋 4. 一鍵複製與免登入 PDF 匯出
支援一鍵複製推算結果字串至剪貼簿，亦可直接點擊列印按鈕輸出純淨 PDF 工作報表。
🔄 5. 多情景敏感度動態對比
建議針對極端值與多組預期情景分別試算，觀察輸出數據的波動區間，輔助做出更穩健的決策。
🛡️ 6. 專業諮詢與日常參考免責聲明
本工具運算結果供日常排程、學業研習與事前參考之用，如涉及重大法規或投資決策請諮詢持證專家。