Camera Stops at 4pm
A 1st AC on a corporate shoot loads four 128GB CFexpress cards into a Canon C70 for a 10-hour day. The producer estimated that XF-AVC 4K at 160 Mbps is a modest codec. By hour 6 the third card is almost full. The DIT has not started the midday offload because the card reader is at the production truck, and the truck is locked while the producer is at lunch.
The camera stops for 40 minutes while a PA hunts for the producer and the keys. The production loses two setups, not because the codec was higher than expected, but because the card count was calculated as storage divided by capacity. It ignored the rotation set: the cards that must stay in the camera while the others are offloading.
This post gives a card-count formula that includes data rate, usable capacity, a safety margin, and the rotation set. By the end, you can size a card order for any shoot before the rental house opens.
The numbers draw from manufacturer codec specifications for Canon, Sony, RED, and Blackmagic, and from the real-world copy and verification times measured by DIT carts. You can verify the Canon C70 data rates directly from Canon's published EOS C70 specifications.
The Card Count Formula
Card count is not a single division problem. It has four parts.
- Total data for the day.
- Usable card capacity.
- A safety margin.
- A rotation set.
Total data (GB) = bitrate (Mbps) × recording hours × 0.45
The constant 0.45 comes from converting megabits per second to gigabytes per hour. One megabit per second sustained for one hour is roughly 0.45 GB. For example, a 160 Mbps codec records about 72 GB per hour and 720 GB over 10 hours.
If you prefer the exact form: total data (GB) = (bitrate ÷ 8) × 3,600 × hours ÷ 1,024. The 0.45 shortcut is close enough for rental orders and rounds up slightly, which adds a small safety buffer.
Base cards = total data ÷ card capacity, rounded up
Use the labeled card capacity for this step, then adjust for usable capacity later. A 128GB CFexpress card often delivers only 118GB to 120GB of usable space after formatting. A 256GB card delivers about 238GB to 245GB.
Safety cards = base cards × 1.2 to 1.3
A 20% margin covers overcranking, extra takes, and a small schedule overrun. A 30% margin is safer for high-stakes shoots where running out means stopping production.
Rotation set = cards needed to keep shooting while the DIT offloads
If the DIT clears cards in a 60-minute lunch, the rotation set might be 1 card per camera. If the offload cycle is 2 hours or slower, the rotation set must cover that whole window. A common rule is: at least 2 cards, or 20% of the total, whichever is larger.
Worked example: Canon C70, XF-AVC 4K, 160 Mbps, 10-hour day, 128GB CFexpress cards
Total data: 160 × 10 × 0.45 = 720 GB.
Base cards: 720 ÷ 128 = 5.6.
Safety at 20%: 5.6 × 1.2 = 6.72 → 7 cards.
Rotation set: 2 cards.
Total order: 9 cards.
If you size cards based on the label only, 6 cards looks right. Once you add safety and rotation, the order is 9. That is the difference between a smooth day and a 4pm stop.
Three Real-World Examples
Example 1: Wedding on Sony A7S III, 100 Mbps XAVC S, 8 hours, 64GB SD cards
Total data: 100 × 8 × 0.45 = 360 GB.
Base cards: 360 ÷ 64 = 5.6.
Safety at 20%: 5.6 × 1.2 = 6.72 → 7 cards.
Rotation set: 2 cards.
Total order: 9 cards.
The couple books a two-camera package, so the final order is 18 cards for both bodies. The DIT offloads during the reception and the rotation set is reused by the last dance.
Example 2: Commercial on RED Komodo, 280 MB/s R3D, 6 hours, 480GB CFast cards
Total data: 280 × 3,600 × 6 ÷ 1,024 = 5,906 GB, or about 5.9 TB.
Base cards: 5,906 ÷ 480 = 12.3.
Safety at 20%: 12.3 × 1.2 = 14.76 → 15 cards.
Rotation set: 3 cards.
Total order: 18 cards.
The commercial is shot on a stage with a DIT cart, so the 3-card rotation set covers the time it takes to clone and verify a 480GB card before it goes back into the camera.
Example 3: Corporate on Canon C70, 160 Mbps XF-AVC, 4 hours, 128GB CFexpress
Total data: 160 × 4 × 0.45 = 288 GB.
Base cards: 288 ÷ 128 = 2.25.
Safety at 20%: 2.25 × 1.2 = 2.7 → 3 cards.
Rotation set: 1 card.
Total order: 4 cards.
The producer rents 4 cards for the day, keeps 1 in rotation, and stores the offloaded cards in a separate pouch before they are reformatted.
Card Count by Camera and Card Capacity
The table below shows how many cards a single camera needs for an 8-hour recording day before any safety or rotation set is added. Add 20% and the rotation set on top of these numbers.
| Camera / Codec | Data Rate | 64GB Cards | 128GB Cards | 256GB Cards | 480GB Cards |
|---|---|---|---|---|---|
| Sony A7S III (100 Mbps) | 45 GB/hr | 8 | 4 | 2 | 1 |
| Canon C70 (160 Mbps) | 72 GB/hr | 13 | 7 | 4 | 2 |
| BMPCC 6K Pro (BRAW 3:1) | ~300 GB/hr | 42 | 21 | 11 | 6 |
| RED Komodo (REDCODE HQ) | ~1 TB/hr | 150 | 75 | 38 | 20 |
The RED Komodo row is why high-bitrate RAW shoots rarely operate on cards alone. A 4-hour day would need 75 128GB cards before safety. Those productions plan around near-continuous offload or on-camera SSD recording, and they size the card pool to cover only the offload interval, not the entire day.
How to Calculate Your Card Count Before the Shoot
- Find the camera's data rate for the codec, resolution, and frame rate. Use the camera's manual or the manufacturer spec sheet, not the menu summary alone.
- Estimate total recording hours for the day. Multiply the scheduled production hours by the expected shooting ratio.
- Calculate total GB: bitrate (Mbps) × hours × 0.45.
- Divide by the card capacity to get the base card count. Round up to the next whole card.
- Add 20% to 30% for safety and overcranking.
- Add the rotation set: enough cards to keep shooting while the DIT offloads and verifies.
At the end of this process you have a card count per camera, per day, with a defined safety margin and a realistic rotation set. That is the number to put on the rental order.
Pro Tips and Common Mistakes
Pro Tip: Use smaller cards for high-stakes shoots. If one card fails, you lose less footage than if an entire day lived on a single 2TB card.
Pro Tip: Match card speed to the camera's write requirement. A V30 SD card cannot sustain a 400 Mbps codec. Check the camera's required sustained write speed and the card's sustained write speed, not the peak read speed on the package.
Pro Tip: Run the Media Offload Time Calculator before you confirm the card strategy. A 128GB CFexpress card can take 15 minutes to copy and verify on a fast reader, or 40 minutes on a slow USB-C reader. That difference determines whether one lunch clears the pool or whether you need a second DIT station.
Common Mistake: Buying cards based on the camera menu listing without checking the actual bitrate for the selected codec and resolution. A Canon C70 set to XF-AVC 4K 160 Mbps needs a different card order than the same camera set to Cinema RAW Light at 600 Mbps. Verify the exact Mbps before ordering.
Common Mistake: Not accounting for offload time. If the DIT takes 2 hours to clear cards, you need enough cards to shoot through that window. The rotation set is not a luxury; it is the bridge between one card coming out of the camera and the same card going back in clean.
Frequently Asked Questions
Can I reuse cards on the same day?
Yes, once they are offloaded and verified. Plan the rotation so you always have clean cards ready before the camera needs them. Never reformat a card until the offload has been verified by checksum or at least by a second copy.
Should I use one big card or many small cards?
Many small cards reduce the risk of losing an entire day if one card corrupts. Big cards are more convenient and mean fewer swaps on long takes. For documentaries with continuous coverage, larger cards win. For narrative work where each take matters, smaller cards with more frequent swaps reduce risk.
How do I know if a card is fast enough?
Check the camera's required sustained write speed against the card's sustained write speed. The read speed on the label is not the number that matters on set. A card that reads fast but writes slowly can drop frames or fail to record high-bitrate codecs.
What is a safe rotation set?
At least 2 cards, or 20% of the total card order, whichever is larger. More if the offload cycle is slow. On multi-day remote shoots where cards cannot be cleared until wrap, the rotation set expands to cover the full unbroken shooting period.
Do I need different cards for different codecs?
You need the card capacity and speed to match the codec. Some cameras require specific card types: CFexpress Type B, CFast 2.0, Sony XQD, or SD V90. The card type is not interchangeable unless the camera supports both slots.
Related Tools
The Storage and Footage Calculator computes total acquisition data from codec, bitrate, and recording hours. The Data Rate Calculator finds the real data rate for your selected codec and resolution. The Media Offload Time Calculator estimates how long it takes to clear cards and plan the rotation set.
For the full picture of production storage planning, Why Your Storage Estimate Was Wrong: The Variables Most Calculators Ignore covers backup strategy, archive, and why acquisition data is only a fraction of the total. For codec-specific bitrates, Video Codecs Explained breaks down every major acquisition format.
Conclusion
Card count is not just storage divided by capacity. It is storage plus safety plus rotation plus offload time. The 1st AC who runs out of cards at 4pm usually made the same error: the count was right on paper but wrong in the workflow.
This post covers capacity planning for single-camera and small multi-camera shoots. Card reliability, write speed, and reader quality are separate issues that can also stop production.
What is the most cards you have ever burned through in a single day, and did you run out?
