diff --git a/src/bin/d18p1.rs b/src/bin/d18p1.rs
new file mode 100644
index 0000000..d22b02a
--- /dev/null
+++ b/src/bin/d18p1.rs
@@ -0,0 +1,7 @@
+use aoc22::{day18, util};
+
+pub fn main() {
+    let droplet = day18::parse_droplet(&util::parse_input());
+
+    println!("Surface area: {}", day18::surface_area(&droplet));
+}
diff --git a/src/day18.rs b/src/day18.rs
new file mode 100644
index 0000000..75bcd90
--- /dev/null
+++ b/src/day18.rs
@@ -0,0 +1,123 @@
+use itertools::Itertools;
+
+pub fn parse_droplet(input: &String) -> Vec<Vec<Vec<bool>>> {
+    let mut cubes: Vec<(usize, usize, usize)> = Vec::new();
+
+    for line in input.lines() {
+        if line.is_empty() {
+            break;
+        }
+
+        let mut sp = line.split(',');
+        cubes.push((
+            sp.next().unwrap().parse().unwrap(),
+            sp.next().unwrap().parse().unwrap(),
+            sp.next().unwrap().parse().unwrap(),
+        ));
+    }
+
+    let (x_min, x_max) = cubes.iter().map(|c| c.0).minmax().into_option().unwrap();
+    let (y_min, y_max) = cubes.iter().map(|c| c.1).minmax().into_option().unwrap();
+    let (z_min, z_max) = cubes.iter().map(|c| c.2).minmax().into_option().unwrap();
+    let x_len = x_max - x_min + 1;
+    let y_len = y_max - y_min + 1;
+    let z_len = z_max - z_min + 1;
+
+    let mut result = vec![vec![vec![false; z_len]; y_len]; x_len];
+    for (x, y, z) in cubes {
+        result[x - x_min][y - y_min][z - z_min] = true;
+    }
+
+    result
+}
+
+pub fn surface_area(droplet: &Vec<Vec<Vec<bool>>>) -> usize {
+    let x_len = droplet.len();
+    assert!(x_len > 0);
+    let y_len = droplet[0].len();
+    assert!(y_len > 0);
+    let z_len = droplet[0][0].len();
+    assert!(z_len > 0);
+
+    let up = (0..x_len)
+        .flat_map(|x| {
+            (0..y_len)
+                .map(move |y| (x, y, (0..z_len).collect()))
+                .collect_vec()
+        })
+        .collect();
+    let down = (0..x_len)
+        .flat_map(|x| {
+            (0..y_len)
+                .map(move |y| (x, y, (0..z_len).rev().collect()))
+                .collect_vec()
+        })
+        .collect();
+    let left = (0..x_len)
+        .flat_map(|x| {
+            (0..z_len)
+                .map(move |z| (x, z, (0..y_len).collect()))
+                .collect_vec()
+        })
+        .collect();
+    let right = (0..x_len)
+        .flat_map(|x| {
+            (0..z_len)
+                .map(move |z| (x, z, (0..y_len).rev().collect()))
+                .collect_vec()
+        })
+        .collect();
+    let fore = (0..y_len)
+        .flat_map(|y| {
+            (0..z_len)
+                .map(move |z| (y, z, (0..x_len).collect()))
+                .collect_vec()
+        })
+        .collect();
+    let back = (0..y_len)
+        .flat_map(|y| {
+            (0..z_len)
+                .map(move |z| (y, z, (0..x_len).rev().collect()))
+                .collect_vec()
+        })
+        .collect();
+
+    let mut result = 0;
+    result += surface_area_dir(droplet, &up, ArgOrder::XYZ);
+    result += surface_area_dir(droplet, &down, ArgOrder::XYZ);
+    result += surface_area_dir(droplet, &left, ArgOrder::XZY);
+    result += surface_area_dir(droplet, &right, ArgOrder::XZY);
+    result += surface_area_dir(droplet, &fore, ArgOrder::YZX);
+    result += surface_area_dir(droplet, &back, ArgOrder::YZX);
+
+    result
+}
+
+enum ArgOrder {
+    XYZ,
+    XZY,
+    YZX,
+}
+
+fn surface_area_dir(
+    droplet: &Vec<Vec<Vec<bool>>>,
+    lines: &Vec<(usize, usize, Vec<usize>)>,
+    order: ArgOrder,
+) -> usize {
+    let mut result = 0;
+    for (a, b, c_range) in lines {
+        let mut last_empty = true;
+        for c in c_range {
+            let occupied = match order {
+                ArgOrder::XYZ => droplet[*a][*b][*c],
+                ArgOrder::XZY => droplet[*a][*c][*b],
+                ArgOrder::YZX => droplet[*c][*a][*b],
+            };
+            if last_empty && occupied {
+                result += 1;
+            }
+            last_empty = !occupied;
+        }
+    }
+    result
+}
diff --git a/src/lib.rs b/src/lib.rs
index ff93375..8ca45b8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@ pub mod day14;
 pub mod day15;
 pub mod day16;
 pub mod day17;
+pub mod day18;
 pub mod day2;
 pub mod day3;
 pub mod day4;