diff --git a/modules/processing.py b/modules/processing.py
index 100a259f8..a75b9f847 100644
--- a/modules/processing.py
+++ b/modules/processing.py
@@ -501,17 +501,15 @@ def process_images(p: StableDiffusionProcessing) -> Processed:
 
 class StableDiffusionProcessingTxt2Img(StableDiffusionProcessing):
     sampler = None
-    firstphase_width = 0
-    firstphase_height = 0
-    firstphase_width_truncated = 0
-    firstphase_height_truncated = 0
 
-    def __init__(self, enable_hr=False, denoising_strength=0.75, firstphase_width=512, firstphase_height=512, **kwargs):
+    def __init__(self, enable_hr=False, denoising_strength=0.75, firstphase_width=0, firstphase_height=0, **kwargs):
         super().__init__(**kwargs)
         self.enable_hr = enable_hr
         self.denoising_strength = denoising_strength
         self.firstphase_width = firstphase_width
         self.firstphase_height = firstphase_height
+        self.truncate_x = 0
+        self.truncate_y = 0
 
     def init(self, all_prompts, all_seeds, all_subseeds):
         if self.enable_hr:
@@ -520,6 +518,32 @@ class StableDiffusionProcessingTxt2Img(StableDiffusionProcessing):
             else:
                 state.job_count = state.job_count * 2
 
+            if self.firstphase_width == 0 or self.firstphase_height == 0:
+                desired_pixel_count = 512 * 512
+                actual_pixel_count = self.width * self.height
+                scale = math.sqrt(desired_pixel_count / actual_pixel_count)
+                self.firstphase_width = math.ceil(scale * self.width / 64) * 64
+                self.firstphase_height = math.ceil(scale * self.height / 64) * 64
+                firstphase_width_truncated = int(scale * self.width)
+                firstphase_height_truncated = int(scale * self.height)
+
+            else:
+                self.extra_generation_params["First pass size"] = f"{self.firstphase_width}x{self.firstphase_height}"
+
+                width_ratio = self.width / self.firstphase_width
+                height_ratio = self.height / self.firstphase_height
+
+                if width_ratio > height_ratio:
+                    firstphase_width_truncated = self.firstphase_width
+                    firstphase_height_truncated = self.firstphase_width * self.height / self.width
+                else:
+                    firstphase_width_truncated = self.firstphase_height * self.width / self.height
+                    firstphase_height_truncated = self.firstphase_height
+
+            self.truncate_x = int(self.firstphase_width - firstphase_width_truncated) // opt_f
+            self.truncate_y = int(self.firstphase_height - firstphase_height_truncated) // opt_f
+
+
     def sample(self, conditioning, unconditional_conditioning, seeds, subseeds, subseed_strength):
         self.sampler = sd_samplers.create_sampler_with_index(sd_samplers.samplers, self.sampler_index, self.sd_model)
 
@@ -528,23 +552,10 @@ class StableDiffusionProcessingTxt2Img(StableDiffusionProcessing):
             samples = self.sampler.sample(self, x, conditioning, unconditional_conditioning)
             return samples
 
-        self.extra_generation_params["First pass size"] = f"{self.firstphase_width}x{self.firstphase_height}"
-
         x = create_random_tensors([opt_C, self.firstphase_height // opt_f, self.firstphase_width // opt_f], seeds=seeds, subseeds=subseeds, subseed_strength=self.subseed_strength, seed_resize_from_h=self.seed_resize_from_h, seed_resize_from_w=self.seed_resize_from_w, p=self)
         samples = self.sampler.sample(self, x, conditioning, unconditional_conditioning)
 
-        truncate_x = 0
-        truncate_y = 0
-        width_ratio = self.width/self.firstphase_width
-        height_ratio = self.height/self.firstphase_height
-
-        if width_ratio > height_ratio:
-            truncate_y = int((self.width - self.firstphase_width) / width_ratio / height_ratio / opt_f)
-
-        elif width_ratio < height_ratio:
-            truncate_x = int((self.height - self.firstphase_height) / width_ratio / height_ratio / opt_f)
-                
-        samples = samples[:, :, truncate_y//2:samples.shape[2]-truncate_y//2, truncate_x//2:samples.shape[3]-truncate_x//2]
+        samples = samples[:, :, self.truncate_y//2:samples.shape[2]-self.truncate_y//2, self.truncate_x//2:samples.shape[3]-self.truncate_x//2]
 
         decoded_samples = decode_first_stage(self.sd_model, samples)
 
diff --git a/modules/ui.py b/modules/ui.py
index 6d1939557..a1d18be91 100644
--- a/modules/ui.py
+++ b/modules/ui.py
@@ -567,8 +567,8 @@ def create_ui(wrap_gradio_gpu_call):
                     enable_hr = gr.Checkbox(label='Highres. fix', value=False)
 
                 with gr.Row(visible=False) as hr_options:
-                    firstphase_width = gr.Slider(minimum=64, maximum=1024, step=64, label="First pass width", value=512)
-                    firstphase_height = gr.Slider(minimum=64, maximum=1024, step=64, label="First pass height", value=512)
+                    firstphase_width = gr.Slider(minimum=0, maximum=1024, step=64, label="First pass width", value=0)
+                    firstphase_height = gr.Slider(minimum=0, maximum=1024, step=64, label="First pass height", value=0)
                     denoising_strength = gr.Slider(minimum=0.0, maximum=1.0, step=0.01, label='Denoising strength', value=0.7)
 
                 with gr.Row(equal_height=True):