作为程序员，没有合适的工具，就得手搓一个，PC端，移动端均可适用。废话不多说，直接上代码。

HTML:

<div class="calculator"><label for="radius">圆的半径 (r)：</label> <input id="radius" type="number" placeholder="输入圆的半径"> <label for="angle">圆心角 (θ，以弧度为单位)：</label> <input id="angle" type="number" placeholder="输入圆心角（单位：弧度）"><button onclick="calculateArcLength()">计算弧长</button><div id="result" class="result">弧长结果将显示在这里</div></div>

JS:

function calculateArcLength() {
        const radius = parseFloat(document.getElementById('radius').value);
        const angle = parseFloat(document.getElementById('angle').value);
        
        if (isNaN(radius) || isNaN(angle) || radius <= 0 || angle <= 0) {
            document.getElementById('result').textContent = "请输入有效的半径和圆心角。";
            return;
        }
        
        const arcLength = radius * angle;
        document.getElementById('result').textContent = `弧长为：${arcLength.toFixed(2)} 单位长度`;
    }

CSS:

.calculator {
    width: 300px;
    background-color: #333;
    color: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
}


label {
    display: block;
    margin-bottom: 10px;
    font-size: 16px;
}

input, select {
    width: 100%!important;
    padding: 10px!important;
    margin-bottom: 20px;
       color: #000000; 
    border-radius: 5px;
    border: 1px solid #555;
    font-size: 16px!important;
    background-color: #ffffff!important;
}

button {
    width: 100%;
    padding: 10px;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 16px;
}

button:hover {
    background-color: orange;
}

.result {
    margin-top: 20px;
    text-align: center;
        font-size: 18px;
}

option {
        background-color: #ffffff;
}


p {
    font-size: 18px;
        margin-top: 5px!important;
}

线上运行，可以直接打开：弧长计算器