diff --git a/README.md b/README.md
index c27c713..094ec4a 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,7 @@ Step-level `uses:` must be the absolute URL. Gitea resolves short refs against g
 |---|---|
 | `{{BUILD_VAR_COMMIT_SHA_SHORT}}` | first 7 chars of `GITHUB_SHA` |
 | `{{BUILD_VAR_BUILD_DATE}}` | UTC, ISO 8601: `%Y-%m-%dT%H:%M:%SZ` |
+| `{{BUILD_VAR_REF_LABEL}}` | `pr-<n>` for pull requests, otherwise `GITHUB_REF_NAME` with `/` → `-`. This matches the [docker-build](https://git.custom-coding.net/templates/docker-build) image tag. |
 | `{{BUILD_VAR_GITHUB_SHA}}` | `GITHUB_SHA` |
 | `{{BUILD_VAR_GITHUB_REF_NAME}}` | `GITHUB_REF_NAME` |
 | `{{BUILD_VAR_GITHUB_REF_TYPE}}` | `GITHUB_REF_TYPE` |
diff --git a/action.yml b/action.yml
index f718393..e5ed12e 100644
--- a/action.yml
+++ b/action.yml
@@ -13,6 +13,16 @@ runs:
         SHA_SHORT="${GITHUB_SHA:0:7}"
         BUILD_DATE="$(date -u '+%Y-%m-%dT%H:%M:%SZ')"
 
+        # Same label as the docker-build image tag: pr-<n> for PRs, else ref name with / -> -
+        REF="${GITHUB_REF:-}"
+        if [[ "$REF" == refs/pull/* ]]; then
+          PR_NUM="${REF#refs/pull/}"
+          REF_LABEL="pr-${PR_NUM%%/*}"
+        else
+          REF_NAME="${GITHUB_REF_NAME:-}"
+          REF_LABEL="${REF_NAME//\//-}"
+        fi
+
         declare -A VARS=(
           [BUILD_VAR_GITHUB_SHA]="${GITHUB_SHA:-}"
           [BUILD_VAR_GITHUB_REF_NAME]="${GITHUB_REF_NAME:-}"
@@ -32,6 +42,7 @@ runs:
           [BUILD_VAR_GITEA_ACTIONS_RUNNER_VERSION]="${GITEA_ACTIONS_RUNNER_VERSION:-}"
           [BUILD_VAR_COMMIT_SHA_SHORT]="$SHA_SHORT"
           [BUILD_VAR_BUILD_DATE]="$BUILD_DATE"
+          [BUILD_VAR_REF_LABEL]="$REF_LABEL"
         )
 
         SED_ARGS=()