Buffer Calculator — Buffer Depth & Write Speed

While you shoot, data arrives at burst rate × file size while the card simultaneously drains the buffer at its write speed, so the buffer fills at the NET rate. Frames before the buffer fills ≈ buffer ÷ (file size − write speed ÷ burst rate). For a 2GB (≈1900MB effective) buffer, 50MB RAW files at 10fps and a 90MB/s card writing at ~81MB/s, that is 1900 ÷ (50 − 8.1) ≈ 45 frames — noticeably more than the simple buffer ÷ file size figure of 38, because the card is draining the buffer as you shoot. The faster the card, the bigger the difference.

While shooting, the camera simultaneously writes from buffer to card. A faster card drains the buffer quicker, effectively increasing your burst depth and reducing recovery time between bursts. This is especially important for sports, wildlife and event photography.

Camera manufacturers rarely publish exact buffer sizes. Check your camera manual for rated burst depths at various file formats. You can estimate the buffer by multiplying the rated RAW burst depth by your RAW file size. Typical buffer sizes range from 1GB to 4GB in modern cameras.

Once the buffer fills, shooting continues at the sustained rate — determined by how fast the card can write. Sustained RAW fps = card write speed ÷ RAW file size. A 90 MB/s card (≈81 MB/s after efficiency) with 50MB files sustains only about 1.6 fps, regardless of the camera burst rate. At its rated 90 MB/s it would sustain 1.8 fps, but real-world cards run a little below their rating.