Cost Per Acquisition (CPA) Calculator
From total ad spend and actions (conversions), compute the cost per action — a measure of ad cost-efficiency.
輸入資料
計算結果
重點速覽：CPA = total ad spend / number of actions (any goal: order, sign-up, download). Lower CPA = more efficient. Compare against gross profit per action (e.g. HK$300 profit vs HK$200 CPA = profit). WARNING: CPA ≠ CAC — CPA counts actions (repeatable), CAC counts new customers; numerator should be ad-attributable spend only. Education, not advice.
計算公式
每次行動成本 (CPA) = 總廣告支出 ÷ 行動次數。
$$CPA = \dfrac{\text{Total Ad Spend}}{\text{Number of Actions}}$$使用說明
- Enter the campaign's total spend.
- Enter the number of actions/conversions.
- View the cost per action.
每次行動成本 (CPA) 計算範例
| 情境 | 總廣告支出 | 行動 (轉化) 次數 | CPA |
|---|---|---|---|
| 基準 | HK$60,000 | 300 次 | HK$200.00 |
| 轉化提升 | HK$60,000 | 500 次 | HK$120.00 |
| 支出增加 | HK$90,000 | 300 次 | HK$300.00 |
CPA = 總廣告支出 ÷ 行動次數。在支出相同下，轉化次數越多 CPA 越低；優化落地頁與受眾可有效降低 CPA。
理財情境案例
案例一：計算廣告活動的 CPA
假設某電商投放一波廣告，總支出 60,000 港元，最終帶來 300 筆訂單 (行動/轉化)。
套用公式：CPA = 總廣告支出 ÷ 行動次數 = 60,000 ÷ 300 = 200 港元。
這代表：平均每促成一筆訂單，需付出 200 港元的廣告費。CPA 是否划算，要對照『每筆訂單的毛利』— 若每筆訂單毛利為 350 港元，扣掉 200 元 CPA 後仍有 150 元淨貢獻，廣告有利可圖;若毛利只有 150 元，則 CPA 200 元會虧損，需優化。
案例二：優化轉化率如何壓低 CPA
承上 (支出 60,000)，若透過改善落地頁與受眾定向，把轉化次數從 300 提升到 500：CPA = 60,000 ÷ 500 = 120 港元，比原本的 200 元降低了 40%。
反之，若在轉化次數不變 (300) 下把支出加碼到 90,000：CPA = 90,000 ÷ 300 = 300 港元，成本效益反而變差。
這說明降低 CPA 的關鍵不在於『少花錢』或『多花錢』,而在於『提升每一元支出的轉化效率』— 優化廣告素材、受眾精準度、落地頁體驗與轉化漏斗，都能在支出不變下拉低 CPA，是行銷投放的核心目標。
常見問題
What is the difference between CPA and CAC?
They are related but differ in focus. CPA is cost per action — one customer may contribute many actions. CAC is cost per new customer — the denominator counts only newly acquired customers. Use CPA for per-conversion cost; CAC for the cost to win a customer.
What is an acceptable CPA?
Compare with the value per action. If gross profit per order exceeds CPA, you profit; otherwise you lose. Practically, derive a 'maximum acceptable CPA' from gross profit and use it as a bidding cap, then keep optimising.
How do I lower CPA?
Mainly by raising conversion rate and targeting precision: better creative and audiences, improved landing page and checkout, cutting poor channels/keywords. A higher conversion rate yields more actions for the same budget, lowering CPA. Pair with the conversion-rate calculator.
How do CPA, CPC and CPM differ?
They measure cost at different funnel stages. CPM (cost per mille) = cost per 1,000 impressions (top, reach). CPC = cost per click (middle, traffic). CPA = cost per action (bottom, actual outcome). Typically CPM < CPC < CPA; they convert: CPC = CPM / (clicks per 1,000 impressions), CPA = CPC / conversion rate. CPA is what you judge against gross profit.
Is CPA the same as CAC?
Close but not identical. CPA's 'action' is a broad, customisable goal (download, sign-up, add-to-cart) and its cost is usually only the ad spend. CAC is strictly the cost to acquire a paying customer and often includes wider costs (team salaries, tools, sales). So CAC is usually higher than ad CPA. Use CPA for single-campaign efficiency, CAC for business health (vs LTV, with LTV/CAC ≥ 3 a common rule).
相關工具
參考資料
內容審核：香港計算器財經團隊。計算邏輯與公式參考香港金融管理局（HKMA）及投資者及理財教育委員會（IFEC）之個人理財計算指引，結果僅供參考，實際以相關機構公佈為準。