diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 41db2a06138..dce07644fab 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -142,6 +142,9 @@ API Changes
   The default implementation allocates an ew byte array and call StoredFieldVisitor#binaryField(FieldInfo, byte[]).
   (Ignacio Vera)
 
+* GITHUB#12592: Add RandomAccessInput#length method to the RandomAccessInput interface. In addition deprecate
+  ByteBuffersDataInput#size in favour of this new method. (Ignacio Vera)
+
 New Features
 ---------------------
 (No changes)
diff --git a/lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/store/EndiannessReverserIndexInput.java b/lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/store/EndiannessReverserIndexInput.java
index b0a2b3ad57e..5ec1402efc7 100644
--- a/lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/store/EndiannessReverserIndexInput.java
+++ b/lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/store/EndiannessReverserIndexInput.java
@@ -96,6 +96,11 @@ final class EndiannessReverserIndexInput extends FilterIndexInput {
       this.in = in;
     }
 
+    @Override
+    public long length() {
+      return in.length();
+    }
+
     @Override
     public byte readByte(long pos) throws IOException {
       return in.readByte(pos);
diff --git a/lucene/core/src/java/org/apache/lucene/store/ByteBuffersDataInput.java b/lucene/core/src/java/org/apache/lucene/store/ByteBuffersDataInput.java
index fdc11381548..1fac3fe9379 100644
--- a/lucene/core/src/java/org/apache/lucene/store/ByteBuffersDataInput.java
+++ b/lucene/core/src/java/org/apache/lucene/store/ByteBuffersDataInput.java
@@ -42,7 +42,7 @@ public final class ByteBuffersDataInput extends DataInput
   private final LongBuffer[] longBuffers;
   private final int blockBits;
   private final int blockMask;
-  private final long size;
+  private final long length;
   private final long offset;
 
   private long pos;
@@ -71,19 +71,25 @@ public final class ByteBuffersDataInput extends DataInput
       this.blockMask = (1 << blockBits) - 1;
     }
 
-    long size = 0;
+    long length = 0;
     for (ByteBuffer block : blocks) {
-      size += block.remaining();
+      length += block.remaining();
     }
-    this.size = size;
+    this.length = length;
 
     // The initial "position" of this stream is shifted by the position of the first block.
     this.offset = blocks[0].position();
     this.pos = offset;
   }
 
+  /**
+   * Returns the total number of bytes in this stream.
+   *
+   * @deprecated Use {@link #length()} instead.
+   */
+  @Deprecated
   public long size() {
-    return size;
+    return length();
   }
 
   @Override
@@ -102,7 +108,7 @@ public final class ByteBuffersDataInput extends DataInput
       pos++;
       return v;
     } catch (IndexOutOfBoundsException e) {
-      if (pos >= size()) {
+      if (pos >= length()) {
         throw new EOFException();
       } else {
         throw e; // Something is wrong.
@@ -135,7 +141,7 @@ public final class ByteBuffersDataInput extends DataInput
         len -= chunk;
       }
     } catch (BufferUnderflowException | ArrayIndexOutOfBoundsException e) {
-      if (pos >= size()) {
+      if (pos >= length()) {
         throw new EOFException();
       } else {
         throw e; // Something is wrong.
@@ -162,7 +168,7 @@ public final class ByteBuffersDataInput extends DataInput
         off += chunk;
       }
     } catch (BufferUnderflowException | ArrayIndexOutOfBoundsException e) {
-      if (pos >= size()) {
+      if (pos >= length()) {
         throw new EOFException();
       } else {
         throw e; // Something is wrong.
@@ -206,6 +212,11 @@ public final class ByteBuffersDataInput extends DataInput
     }
   }
 
+  @Override
+  public long length() {
+    return length;
+  }
+
   @Override
   public byte readByte(long pos) {
     pos += offset;
@@ -287,7 +298,7 @@ public final class ByteBuffersDataInput extends DataInput
         off += chunk;
       }
     } catch (BufferUnderflowException | IndexOutOfBoundsException e) {
-      if (pos - offset + Float.BYTES > size()) {
+      if (pos - offset + Float.BYTES > length()) {
         throw new EOFException();
       } else {
         throw e; // Something is wrong.
@@ -319,7 +330,7 @@ public final class ByteBuffersDataInput extends DataInput
         off += chunk;
       }
     } catch (BufferUnderflowException | IndexOutOfBoundsException e) {
-      if (pos - offset + Long.BYTES > size()) {
+      if (pos - offset + Long.BYTES > length()) {
         throw new EOFException();
       } else {
         throw e; // Something is wrong.
@@ -359,8 +370,8 @@ public final class ByteBuffersDataInput extends DataInput
 
   public void seek(long position) throws EOFException {
     this.pos = position + offset;
-    if (position > size()) {
-      this.pos = size();
+    if (position > length()) {
+      this.pos = length();
       throw new EOFException();
     }
   }
@@ -375,7 +386,7 @@ public final class ByteBuffersDataInput extends DataInput
   }
 
   public ByteBuffersDataInput slice(long offset, long length) {
-    if (offset < 0 || length < 0 || offset + length > this.size) {
+    if (offset < 0 || length < 0 || offset + length > this.length) {
       throw new IllegalArgumentException(
           String.format(
               Locale.ROOT,
@@ -393,7 +404,7 @@ public final class ByteBuffersDataInput extends DataInput
     return String.format(
         Locale.ROOT,
         "%,d bytes, block size: %,d, blocks: %,d, position: %,d%s",
-        size(),
+        length(),
         blockSize(),
         blocks.length,
         position(),
diff --git a/lucene/core/src/java/org/apache/lucene/store/IndexInput.java b/lucene/core/src/java/org/apache/lucene/store/IndexInput.java
index 3d3d90bd6ff..9e482b7e429 100644
--- a/lucene/core/src/java/org/apache/lucene/store/IndexInput.java
+++ b/lucene/core/src/java/org/apache/lucene/store/IndexInput.java
@@ -148,6 +148,12 @@ public abstract class IndexInput extends DataInput implements Closeable {
     } else {
       // return default impl
       return new RandomAccessInput() {
+        @Override
+        public long length() {
+          assert length == slice.length();
+          return slice.length();
+        }
+
         @Override
         public byte readByte(long pos) throws IOException {
           slice.seek(pos);
diff --git a/lucene/core/src/java/org/apache/lucene/store/RandomAccessInput.java b/lucene/core/src/java/org/apache/lucene/store/RandomAccessInput.java
index 3c735065d33..3578b2b13b2 100644
--- a/lucene/core/src/java/org/apache/lucene/store/RandomAccessInput.java
+++ b/lucene/core/src/java/org/apache/lucene/store/RandomAccessInput.java
@@ -25,6 +25,9 @@ import org.apache.lucene.util.BitUtil; // javadocs
  */
 public interface RandomAccessInput {
 
+  /** The number of bytes in the file. */
+  public long length();
+
   /**
    * Reads a byte at the given position in the file
    *
diff --git a/lucene/test-framework/src/java/org/apache/lucene/tests/store/BaseDirectoryTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/tests/store/BaseDirectoryTestCase.java
index 42d8d9bea3e..cdb8b5d983d 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/tests/store/BaseDirectoryTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/tests/store/BaseDirectoryTestCase.java
@@ -955,6 +955,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       // slice
       IndexInput input = dir.openInput("longs", newIOContext(random()));
       RandomAccessInput slice = input.randomAccessSlice(0, input.length());
+      assertEquals(input.length(), slice.length());
       for (int i = 0; i < longs.length; i++) {
         assertEquals(longs[i], slice.readLong(i * 8L));
       }
@@ -963,6 +964,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       for (int i = 1; i < longs.length; i++) {
         long offset = i * 8L;
         RandomAccessInput subslice = input.randomAccessSlice(offset, input.length() - offset);
+        assertEquals(input.length() - offset, subslice.length());
         for (int j = i; j < longs.length; j++) {
           assertEquals(longs[j], subslice.readLong((j - i) * 8L));
         }
@@ -980,6 +982,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
         o.close();
         IndexInput padded = dir.openInput(name, newIOContext(random()));
         RandomAccessInput whole = padded.randomAccessSlice(i, padded.length() - i);
+        assertEquals(padded.length() - i, whole.length());
         for (int j = 0; j < longs.length; j++) {
           assertEquals(longs[j], whole.readLong(j * 8L));
         }
@@ -1004,6 +1007,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       // slice
       IndexInput input = dir.openInput("ints", newIOContext(random()));
       RandomAccessInput slice = input.randomAccessSlice(0, input.length());
+      assertEquals(input.length(), slice.length());
       for (int i = 0; i < ints.length; i++) {
         assertEquals(ints[i], slice.readInt(i * 4L));
       }
@@ -1012,6 +1016,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       for (int i = 1; i < ints.length; i++) {
         long offset = i * 4L;
         RandomAccessInput subslice = input.randomAccessSlice(offset, input.length() - offset);
+        assertEquals(input.length() - offset, subslice.length());
         for (int j = i; j < ints.length; j++) {
           assertEquals(ints[j], subslice.readInt((j - i) * 4L));
         }
@@ -1029,6 +1034,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
         o.close();
         IndexInput padded = dir.openInput(name, newIOContext(random()));
         RandomAccessInput whole = padded.randomAccessSlice(i, padded.length() - i);
+        assertEquals(padded.length() - i, whole.length());
         for (int j = 0; j < ints.length; j++) {
           assertEquals(ints[j], whole.readInt(j * 4L));
         }
@@ -1052,6 +1058,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       // slice
       IndexInput input = dir.openInput("shorts", newIOContext(random()));
       RandomAccessInput slice = input.randomAccessSlice(0, input.length());
+      assertEquals(input.length(), slice.length());
       for (int i = 0; i < shorts.length; i++) {
         assertEquals(shorts[i], slice.readShort(i * 2L));
       }
@@ -1060,6 +1067,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       for (int i = 1; i < shorts.length; i++) {
         long offset = i * 2L;
         RandomAccessInput subslice = input.randomAccessSlice(offset, input.length() - offset);
+        assertEquals(input.length() - offset, subslice.length());
         for (int j = i; j < shorts.length; j++) {
           assertEquals(shorts[j], subslice.readShort((j - i) * 2L));
         }
@@ -1077,6 +1085,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
         o.close();
         IndexInput padded = dir.openInput(name, newIOContext(random()));
         RandomAccessInput whole = padded.randomAccessSlice(i, padded.length() - i);
+        assertEquals(padded.length() - i, whole.length());
         for (int j = 0; j < shorts.length; j++) {
           assertEquals(shorts[j], whole.readShort(j * 2L));
         }
@@ -1100,6 +1109,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       // slice
       IndexInput input = dir.openInput("bytes", newIOContext(random()));
       RandomAccessInput slice = input.randomAccessSlice(0, input.length());
+      assertEquals(input.length(), slice.length());
       for (int i = 0; i < bytes.length; i++) {
         assertEquals(bytes[i], slice.readByte(i));
       }
@@ -1108,6 +1118,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       for (int i = 1; i < bytes.length; i++) {
         long offset = i;
         RandomAccessInput subslice = input.randomAccessSlice(offset, input.length() - offset);
+        assertEquals(input.length() - offset, subslice.length());
         for (int j = i; j < bytes.length; j++) {
           assertEquals(bytes[j], subslice.readByte(j - i));
         }
@@ -1125,6 +1136,7 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
         o.close();
         IndexInput padded = dir.openInput(name, newIOContext(random()));
         RandomAccessInput whole = padded.randomAccessSlice(i, padded.length() - i);
+        assertEquals(padded.length() - i, whole.length());
         for (int j = 0; j < bytes.length; j++) {
           assertEquals(bytes[j], whole.readByte(j));
         }