diff --git a/docs/widgets/services/customapi.md b/docs/widgets/services/customapi.md
index 7f26f80fb..c392d942c 100644
--- a/docs/widgets/services/customapi.md
+++ b/docs/widgets/services/customapi.md
@@ -54,12 +54,20 @@ widget:
             time: other key
         color: theme # optional - defaults to "". Allowed values: `["theme", "adaptive", "black", "white"]`.
         format: date # optional
+    - field: key
+      label: Number of things in array
+      format: size
+    # This (no field) will take the root of the API response, e.g. when APIs return an array:
+    - label: Number of items
+      format: size
 ```
 
-Supported formats for the values are `text`, `number`, `float`, `percent`, `bytes`, `bitrate`, `date` and `relativeDate`.
+Supported formats for the values are `text`, `number`, `float`, `percent`, `bytes`, `bitrate`, `size`, `date` and `relativeDate`.
 
 The `dateStyle` and `timeStyle` options of the `date` format are passed directly to [Intl.DateTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/DateTimeFormat) and the `style` and `numeric` options of `relativeDate` are passed to [Intl.RelativeTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat).
 
+The `size` format will return the length of the array or string, or the number of keys in an object. This is then formatted as `number`.
+
 ## Example
 
 For the following JSON object from the API:
diff --git a/src/widgets/customapi/component.jsx b/src/widgets/customapi/component.jsx
index 726dcb602..3f1825b25 100644
--- a/src/widgets/customapi/component.jsx
+++ b/src/widgets/customapi/component.jsx
@@ -9,6 +9,11 @@ function getValue(field, data) {
   let lastField = field;
   let key = "";
 
+  // Support APIs that return arrays or scalars directly.
+  if (typeof field === "undefined") {
+    return value;
+  }
+
   while (typeof lastField === "object") {
     key = Object.keys(lastField)[0] ?? null;
 
@@ -27,6 +32,16 @@ function getValue(field, data) {
   return value[lastField] ?? null;
 }
 
+function getSize(data) {
+  if (Array.isArray(data) || typeof data === "string") {
+    return data.length;
+  } else if (typeof data === "object" && data !== null) {
+    return Object.keys(data).length;
+  }
+
+  return NaN;
+}
+
 function formatValue(t, mapping, rawValue) {
   let value = rawValue;
 
@@ -85,6 +100,9 @@ function formatValue(t, mapping, rawValue) {
         numeric: mapping?.numeric,
       });
       break;
+    case "size":
+      value = t("common.number", { value: getSize(value) });
+      break;
     case "text":
     default:
     // nothing