Introduction
The director wants a 2.39:1 cinemascope framing, but your camera records in 16:9. The colorist needs the exact pixel crop dimensions to apply in DaVinci Resolve before the first round of dailies ships. You're looking at a 3840 by 2160 source file and you need to know exactly how many pixels to trim from top and bottom. Getting this wrong means the framing shifts between editorial and the final grade.
The aspect ratio calculator converts between any two aspect ratios and returns exact pixel dimensions. Enter your source resolution and target ratio, and it handles the arithmetic so your pipeline stays clean from camera through delivery.
What This Tool Calculates
The calculator accepts width in pixels, height in pixels, and a target aspect ratio (entered as two numbers, such as 2.39 and 1). It can also reverse the calculation, taking a target aspect ratio and one dimension to solve for the other.
Outputs include the converted pixel dimensions, the number of pixels cropped or added (pillarbox/letterbox), and the original source aspect ratio expressed as a decimal and as a simplified ratio (such as 16:9 or 1.78:1).
The Formula and How It Works
Aspect ratio is the width of the frame divided by the height. A 3840 by 2160 frame is 3840 / 2160 = 1.778, commonly written as 16:9 or 1.78:1.
To convert from 16:9 to 2.39:1 while preserving the full width: new height = width / target ratio = 3840 / 2.39 = 1607 pixels. The crop is 2160 minus 1607 = 553 pixels total, or 276 pixels from top and 277 from bottom (rounding to the nearest even number for codec compatibility).
To convert while preserving full height: new width = height times target ratio = 2160 times 2.39 = 5162 pixels. Since this exceeds the source width, the image would need pillarboxing or an upscale, which is why width-preserving crops are the standard approach for wider ratios.
The calculator also simplifies ratios using the greatest common divisor (GCD). For 3840 by 2160, the GCD is 120. Dividing both by 120 gives 32:18, which simplifies further to 16:9.
Real-World Examples
Cinemascope Crop for Festival DCP
A post supervisor preparing a DCP for Cannes needed 2.39:1 framing from 4K 16:9 source files. The calculator returned a crop to 3840 by 1607 pixels. The even-number rounding to 1606 pixels ensured H.264 and H.265 codec compatibility. The crop template was applied as a Resolve Power Window across all 847 shots in the timeline.
Vertical Reformat for Social Media
A production company repurposing a 2.39:1 feature film trailer for Instagram Reels (9:16) used the calculator to determine the center crop. From a 3840 by 1607 cinemascope frame, a 9:16 extraction at full height produced a crop of 904 by 1607 pixels. The editor used this to set up a pan-and-scan workflow, knowing the exact pixel width available at any reframing position.
LED Wall Stage Pixel Mapping
A virtual production stage running Unreal Engine on a curved LED wall needed to know the exact pixel dimensions for a 2.76:1 Ultra Panavision 70 aspect ratio mapped onto a 7680-pixel-wide display. The calculator returned 7680 by 2783 pixels. The technical director used these dimensions to configure the nDisplay cluster and set the inner frustum camera correctly.
Common Cinema and Broadcast Aspect Ratios
| Name | Ratio | Decimal | Typical Use |
|---|---|---|---|
| Academy | 1.375:1 | 1.375 | Classic 35mm film |
| HDTV | 16:9 | 1.778 | Broadcast, streaming |
| Flat Widescreen | 1.85:1 | 1.85 | US theatrical standard |
| Cinemascope | 2.39:1 | 2.39 | Widescreen theatrical |
| IMAX | 1.43:1 | 1.43 | IMAX 70mm film |
| Vertical Video | 9:16 | 0.5625 | TikTok, Reels, Shorts |
| Ultra Panavision 70 | 2.76:1 | 2.76 | Large-format epic |
Pro Tips and Common Mistakes
Pro Tips
- Always round your final pixel dimensions to even numbers. H.264 and H.265 codecs require width and height divisible by 2. ProRes and DNx prefer multiples of 8 for optimal performance.
- When shooting open gate with the intent to crop in post, frame your composition for the final ratio on set using frame guides. This prevents important elements from landing in the crop zone.
- For dual-delivery projects (theatrical at 2.39:1 and streaming at 16:9), shoot with enough headroom to satisfy both frames. The ARRI ALEXA 65's open gate of 1.55:1 allows comfortable extraction of both ratios from a single negative.
- Pixel aspect ratio (PAR) differs from display aspect ratio. Standard definition formats use non-square pixels. If you're working with SD footage, confirm your PAR before calculating display dimensions.
Common Mistakes
- Confusing 2.35:1 with 2.39:1. The original CinemaScope ratio was 2.35:1, but SMPTE standardized it to 2.39:1 in 1970. Most modern cinemascope deliveries use 2.39:1. Check your deliverable specs to confirm which standard your distributor requires.
- Applying the crop from the top only instead of splitting it between top and bottom. An asymmetric crop shifts the entire frame downward, ruining carefully composed eye lines and horizon placement.
- Forgetting that some cameras record in sensor-native ratios that differ from standard broadcast ratios. The RED V-RAPTOR sensor is 17:9, not 16:9. A 16:9 extraction from 17:9 source requires a slight horizontal crop.
Frequently Asked Questions
What aspect ratio does Netflix require for delivery?
Netflix accepts multiple ratios including 16:9 (1.78:1), 1.85:1, and 2.39:1. The chosen ratio must match what was editorially intended. Netflix does not require a specific ratio but does require that the delivered file matches the creative intent with no unintended letterboxing baked into the image.
How do I convert between 4:3 and 16:9?
To go from 4:3 to 16:9, you either crop the top and bottom (losing 25% of the vertical frame) or add pillarboxing on the sides. To go from 16:9 to 4:3, you crop the sides (losing 25% of the horizontal frame) or add letterboxing on top and bottom. The calculator shows you the exact pixel values for either approach.
What is the difference between letterboxing and pillarboxing?
Letterboxing adds black bars on top and bottom to display a wider image in a narrower frame (such as 2.39:1 content in a 16:9 container). Pillarboxing adds black bars on the left and right to display a narrower image in a wider frame (such as 4:3 content in a 16:9 container).
Can I use non-standard aspect ratios?
Yes. Directors like Wes Anderson and Robert Eggers have used 1.33:1 (The Grand Budapest Hotel) and 1.19:1 (The Lighthouse) for creative effect. The calculator works with any ratio you enter. Confirm with your distributor that their platform supports non-standard ratios before committing.
Start Calculating
Aspect ratio errors cascade through every department in post. Getting the math right at the start of your pipeline saves hours of reframing, re-rendering, and re-delivering. Whether you're cropping for cinemascope or reformatting for social media, this calculator gives you the exact pixel dimensions in seconds.
Run your project's source resolution and target delivery ratio through the calculator above. What aspect ratio are you delivering in, and have you ever caught a crop error after it reached the client?
