Offline Currency Converter – Use Your Own Exchange Rate

How Exchange Rates Work

An exchange rate tells you how much of one currency you get for one unit of another currency. In this tool, the rate is always interpreted as:

1 unit of the From currency equals X units of the To currency.

For example, if you choose USD as the From currency and EUR as the To currency, and you know that:

1 USD = 0.90 EUR

then the correct rate to enter is 0.90. The calculator will multiply the amount in USD by 0.90 to give you the result in EUR.

Because you supply the rate yourself, you can use:

• Rates from a bank or card issuer statement.
• A fixed rate your company provides for reimbursement.
• A rate you noted earlier in the day when you had an internet connection.

Formula Used by the Calculator

The calculator applies a straightforward formula. Let:

• A be the amount in the From currency.
• R be the exchange rate you enter (1 From = R To).
• B be the converted amount in the To currency.

The basic relationship is:

B = A × R

In mathematical notation, this can be written as:

After the multiplication, the tool rounds the result according to the number of decimal places you select (for example, 2, 4, or 6 decimal places). This rounding only affects the display, not the internal logic of the calculation.

Step-by-Step: How to Use This Currency Converter

1. Enter the amount

   In the Amount field, type how much money you have in the From currency. You can use whole numbers or decimals.

2. Select the From currency

   Use the first dropdown (From currency) to choose the currency you are starting with, such as USD, EUR, GBP, JPY, AUD, CAD, or CHF.

3. Select the To currency

   Use the second dropdown (To currency) to choose the currency you want to convert into.

4. Type the exchange rate

   In the exchange rate field, enter how many units of the To currency equal 1 unit of the From currency. The label “1 From = ? To” is a reminder of this direction.

5. Choose decimal places

   Use the decimals selector to choose how many decimal places to show. For everyday spending, 2 decimals is usually enough; for more precise planning, 4 or 6 decimals may be useful.

6. Convert

   Click the convert button. The result panel will show the converted amount in the To currency, rounded to the decimal setting you selected.

7. Optional: Swap directions

   If you want to reverse the conversion (for example, EUR back to USD), use the swap control if available, or manually swap the From and To currencies and use the appropriate inverse rate.

Worked Example

Imagine you are traveling from the United States to the euro area. You have a hotel bill for 150 USD, and your travel policy tells you to use the fixed rate:

1 USD = 0.92 EUR

Here is how you would use the converter:

• Amount: 150
• From currency: USD
• To currency: EUR
• Exchange rate: 0.92 (because 1 USD = 0.92 EUR)
• Decimals: 2

The calculator applies the formula:

Converted amount = 150 × 0.92 = 138

With 2 decimals selected, it will show:

138.00 EUR

If you change the decimal setting to 4 or 6 places, the internal value remains 138, and the display will still effectively show the same value, just with more zeros after the decimal point.

As another example, suppose you are converting 25,000 JPY to USD, using a rate you saw earlier in the day:

1 JPY = 0.0068 USD

• Amount: 25,000
• From currency: JPY
• To currency: USD
• Exchange rate: 0.0068
• Decimals: 2

The calculation is:

25,000 × 0.0068 = 170

The result will be displayed as 170.00 USD at 2 decimal places.

When to Use a Manual Converter vs. a Live-Rate Tool

Manual converters and live-rate converters each have strengths and trade-offs. The table below outlines the main differences.

Use this manual converter when you need privacy, offline operation, or strict control over the rate used. Use a live-rate converter when you specifically need the most recent market rate and a connection is available.

Interpreting the Results

After you click convert, the result field will show the converted amount in the To currency. Keep in mind the following points when reading the output:

• Currency direction – The displayed result is always “From currency converted into To currency” using the rate you entered as “1 From = R To”.
• Rounding – The number of decimal places can slightly change the final displayed amount, especially for large sums or very precise rates.
• No fees included – The amount does not include bank or card fees, foreign transaction charges, or currency exchange commissions.
• Approximation – In real transactions, amounts are often rounded by merchants, banks, or card issuers, so your real charge or payout may differ slightly from the calculator result.

Typical Use Cases

Travel and Everyday Spending

While abroad, you might know the approximate rate from a printed note or from checking earlier in the day. You can use that rate in this tool to quickly estimate:

• How much a restaurant bill is in your home currency.
• The cost of a hotel stay or tour in your budget currency.
• Whether a local cash price is better than paying by card in your home currency.

Business and Expense Reports

Companies often specify a standard rate for internal reporting, which may differ from the live market rate. This converter works well for:

• Filling in expense reports using the official company rate.
• Converting supplier invoices into your reporting currency.
• Checking whether your spreadsheet formulas produce the expected totals.

Personal Budgeting and Online Shopping

Even when you are not traveling, it can be useful to think in another currency:

• Estimating the cost of an online purchase listed in a foreign currency.
• Comparing salaries or budgets between two countries.
• Checking the impact of exchange rate changes on regular transfers.

Limitations, Assumptions, and Disclaimer

To use this converter responsibly, be aware of the following limitations and assumptions:

• User-provided rates only – The tool does not fetch or verify exchange rates. All results depend entirely on the rate you enter. If the rate is out of date or incorrect, the result will also be inaccurate.
• Market changes – Exchange rates can move frequently, sometimes many times per minute. For important decisions, confirm current rates using a trusted financial source such as your bank, card issuer, or a reputable financial data provider.
• No fees or spreads – Real-world conversions often include a spread (difference between buy and sell rates), commission fees, or card surcharges. This calculator assumes no additional fees or spreads, so actual charges or payouts may differ from the displayed result.
• Rounding behavior – Rounding to a small number of decimal places can introduce small differences, especially for large amounts or very precise rates. If precision is critical, consider using more decimal places and double-checking with another method.
• Informational tool – The calculator is provided for general information and convenience. It does not constitute financial, legal, or tax advice, and it should not be used as the sole basis for high-value or legally binding financial decisions.

By using this tool, you accept that the results are approximations and that you remain responsible for confirming important values with reliable sources.

How the Calculator Works Internally

For transparency, here is what happens inside your browser when you run a conversion:

1. The tool reads the amount, the exchange rate, and the desired number of decimals from the form.
2. It multiplies the amount by the exchange rate using standard floating-point arithmetic.
3. The result is rounded to the selected number of decimal places.
4. The rounded value is displayed in the result area as the converted amount.

All of these steps occur on your device. No server processing is required, which helps keep your data private and makes the tool usable even with unreliable or unavailable internet connections.

Related Tools and Further Reading

If you often work with percentages, budgets, or interest calculations, you may find it helpful to use this converter alongside other financial calculators, such as percentage change calculators or budgeting tools. Using a consistent method across tools can make your reports and comparisons more coherent.

For a deeper understanding of how exchange rates are determined and why they change, consider reading introductory guides on topics such as currency markets, bid–ask spreads, and central bank policies from reputable financial education sources.