単位変換
APIなしで30の主要な世界通貨を変換し、ミニレートテーブルも表示します。
このツールについて
USD、EUR、GBP、JPY、CNYなど30の主要な世界通貨間で任意の金額を即座に変換できます。変換にはハードコードされた2025年の概算為替レートを使用するので、APIキー不要で完全にオフラインで動作します。逆レートが結果の下に表示され、選択した通貨が他のすべての通貨と比較されるミニレートテーブルが表示されます。「最終更新日」タイムスタンプでレートの時期が示されます。
使い方
- 1 「金額」フィールドに変換したい金額を入力してください。
- 2 ドロップダウンから元の通貨（From）と目標通貨（To）を選択してください。
- 3 変換された金額と逆レートが即座に表示されます — ボタンのクリックは不要です。
- 4 レートテーブルまでスクロールして、元の通貨が30すべての通貨と比較されているのを確認してください。
An important note about the rates this tool uses
Be clear about one thing up front: this converter does not fetch live exchange rates. It ships with a fixed table of approximate rates relative to the US dollar, captured around early 2025, and it does all its math from that built-in table. The interface even labels this — "Rates last updated: January 2025 (approximate)." The upside is real: because there is no network call, the tool is instant, works completely offline, and sends nothing about your amounts or currencies to any server. The trade-off is equally real: the numbers are a snapshot, not today's market rate, so they are perfect for quick estimates and learning but should never be used for an actual financial transaction, accounting, or anything where being off by a few percent matters.
How the conversion math works
Every currency in the table is stored as its value against 1 US dollar. To convert between any two currencies, the tool routes through USD as a common reference. The formula is simply:
result = amount × (rate_to ÷ rate_from)
where each rate is "how many of that currency equal one USD." This cross-rate approach means you can convert directly between, say, euros and yen without USD ever appearing in the result — USD is just the internal pivot.
A worked example
Suppose the built-in table holds EUR = 0.921 and JPY = 149.50 per US dollar, and you want to convert 200 EUR to JPY. The tool computes 200 × (149.50 ÷ 0.921) ≈ 200 × 162.32 ≈ 32,465 JPY. It also shows you the unit rate both ways — 1 EUR = 162.32 JPY and the inverse 1 JPY = 0.0062 EUR — so you can sanity-check the direction. The rate table below the result then lists 1 EUR against every other supported currency at once, which is handy for comparing several destinations in a single glance.
Smart formatting details
The tool adjusts decimal places to suit each currency, which avoids misleading precision:
| Currency type | Decimals shown | Why |
|---|---|---|
| Yen, Won, Dong, Rupiah, Naira | 0 | These currencies are not normally divided into sub-units in everyday use |
| Large values (≥100) | 2 | Cents-level precision is enough at that scale |
| Small values (<100) | 4 | Extra digits matter when one unit is worth a fraction |
It also prefixes the correct currency symbol (€, ¥, ₹, and so on) and uses the swap button to flip the "from" and "to" fields instantly — useful when you realise you set up the conversion backwards.
Genuine use cases
- Trip budgeting. Get a rough sense of what a hotel price in another currency means in your own before you travel.
- Reading prices online. Quickly estimate what an item listed abroad costs at home.
- Learning relative value. The all-currencies rate table is a fast way to grasp how 1 unit of one currency stacks up against dozens of others.
- Offline estimates. On a plane or with no signal, you still get a usable approximation because the rates are built in.
Common mistakes to avoid
- Treating the result as a live quote. Real rates move every second and your bank adds a margin. For an actual exchange, check your bank or a live-rate service at the moment of the transaction.
- Forgetting the hidden costs of real exchanges. Even a perfect mid-market rate ignores the spread, fees, and ATM or card surcharges you will pay in practice. The true cost of converting money is almost always worse than any reference rate.
- Over-reading the decimals. Four decimal places look precise, but the underlying rate is an approximate snapshot. Trust the order of magnitude, not the last digit.
- Assuming a currency is missing because it is small. The table covers 30 widely used currencies; if you need one outside that set, this tool cannot help with it.
- Using stale rates for volatile currencies. Some currencies move sharply over months. A January-2025 snapshot can drift especially far for high-inflation or rapidly changing currencies, so treat those estimates with extra caution.
In short: this is a fast, private, offline estimator built on a fixed approximate rate table — excellent for ballpark figures and understanding relative value, and deliberately not a substitute for a live market rate when money actually changes hands.