How to Build a Currency Converter App in Streamlit

💡 Why Build a Currency Converter?

We’ve all been there — scrolling through flight deals or ordering something online and wondering: “How much is that in my currency?” Instead of Googling it every time, let’s build a lightweight currency converter app using Streamlit and Fixer.io API.

It’s quick, it’s useful, and it’s a fantastic intro project to:

• Calling external APIs
• Building a real-time UI with Streamlit
• Handling user input and API data

Ready? Let’s go. 🚀

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🛠️ What You’ll Need

Before we dive in, make sure you’ve got the following:

🔧 Prerequisites:

• Python 3.x installed
• Streamlit installed (pip install streamlit)
• A free API key from Fixer.io

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📦 Step 1: Install Required Packages

Open your terminal and run:

pip install streamlit requests

These are the only two packages we need — Streamlit for UI, and requests to fetch data from the API.

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🔑 Step 2: Get Your API Key from Fixer.io

1. Go to https://fixer.io
2. Sign up for a free account
3. Copy your API key from the dashboard

Replace the API key in the code below with your own. (Free plan works just fine for basic currency rates.)

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🧠 Step 3: Set Up Your Script

Create a new file, e.g., currency_converter.py, and start by importing the essentials:

import streamlit as st
import requests

Then define your API endpoint:

API_KEY = "your_api_key_here"
URL = f"http://data.fixer.io/api/latest?access_key={API_KEY}"

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🔄 Step 4: Fetch Exchange Rates

We’ll write a function to make a GET request to Fixer and return exchange rates:

def get_exchange_rates():
    response = requests.get(URL)
    if response.status_code == 200:
        data = response.json()
        if data.get("success"):
            return data["rates"]
        else:
            st.error("Error fetching exchange rates. Please check your API key.")
    else:
        st.error("Failed to fetch exchange rates.")
    return {}

If all goes well, you’ll get a dictionary of rates like {"USD": 1.12, "INR": 89.2, ...}.

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🌍 Step 5: Create a Currency Name Map

Fixer only returns currency codes (e.g., USD, INR). For a better user experience, map them to readable names:

currency_names = {
    "USD": "US Dollar",
    "EUR": "Euro",
    "SAR": "Saudi Riyal",
    "INR": "Indian Rupee",
    "GBP": "British Pound",
    # ... include as many as needed
}

To keep things clean, only show codes that actually exist in the API response.

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🧾 Step 6: Build the Streamlit UI

This is where the magic happens ✨

st.title("Currency Converter")

# User input
amount = st.number_input("Enter amount:", min_value=0.01, value=1.00, format="%.2f")

# Dynamic dropdowns
from_currency = st.selectbox("From Currency:", options=[f"{code} ({name})" for code, name in currency_names.items() if code in fx])
to_currency = st.selectbox("To Currency:", options=[f"{code} ({name})" for code, name in currency_names.items() if code in fx])

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🔁 Step 7: Handle Conversion Logic

When the user hits the Convert button:

if st.button("Convert"):
    from_code = from_currency.split(" ")[0]
    to_code = to_currency.split(" ")[0]
    
    if from_code in fx and to_code in fx:
        converted_amount = round(amount * fx[to_code] / fx[from_code], 2)
        st.success(f"{amount} {from_code} = {converted_amount} {to_code}")
    else:
        st.error("Invalid currency selection. Please try again.")

This takes the input amount, fetches the correct conversion rate, and shows the result.

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📷 (Optional) Step 8: Visual Polish

You can enhance the app further with:

• Icons or flags using images
• Charts showing historical trends (Fixer has historical data APIs too)
• Themes or dark mode (Streamlit has built-in theming)

🚀 Run the App

Open a terminal and run:

streamlit run currency_converter.py

🎉 And voilà — a fully working currency converter in your browser!

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🧠 Wrap-Up

In this tutorial, we learned how to:

• Use Fixer.io API to fetch real-time exchange rates
• Build an interactive Streamlit UI
• Handle user input and show dynamic results

This is a great beginner project to learn APIs and Streamlit. Want to take it further? Try adding:

• Currency trend graphs
• Historical conversions
• Local caching to improve performance

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🙋 FAQ

❓ Is Fixer.io free?

Yes! There’s a free tier with hourly updates for EUR base currency.

❓ Can I change the base currency?

Only with a paid plan — by default, Fixer.io returns rates based on EUR.

❓ Can I convert to/from cryptocurrencies?

Yes, Fixer supports some crypto like BTC, though updates may be less frequent.

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💬 Your Turn!

Did you build this app? Got stuck somewhere or added cool features?

Drop a comment below, or reach out to us at Ossels AI if you want help building real-world AI or data apps like this one.

🔗 Also check out our other Python + AI tutorials here