Backup Full Incremental Size Calculator

A home server organize your digital life, except it’s hard on the storage drive. You’ve got terabytes of data, but never realy know how much space the backup process take up. That determines whether you can actualy get your data back (a disk full error versus successful recovery). With the calculator above, the math gets done for you.

Your vague anxiety over capacity becomes a concrete target size. And we see that backup storage isn’t just a static copy, it is a system that grows with your habits and shrinks with your compression ratios. That’s what it comes down to: the daily change rate.

How to Calculate Your Backup Storage Space

What portion of your data change every day? Maybe not much if you are editing raw photos. (Those don’t change very often!) But if you’re running a database, maybe a lot. (Logging happens all the time.)

The higher the daily churn, the more data accumulate. And the calculator multiplies it by length of your chain: how many incrementals do you have? You might have six per week, with a full one every Sunday. Twenty-nine per month (a full once a month)? The longer the chain, the worse these little changes adds up.

Compression and deduplication keep the total manageable. But they are not as high than you think. Maybe you’ve heard software claim 3x compression rate. That’s true, for uncompressed text files. For everything else: video, encrypted backups? You’re down to 1.0ish. The calculator wants to know those rates, and yes, enter them honest.

When you encrypt something before backing it up, you make the thing unique on a per-block basis making deduplication impossible. In exchange for security, you sacrifice storage efficiency. And that is what everyone gets wrong with their drive sizes.

Then there’s retention. Why do you have a single backup set? Because you might accidental delete something from that set. And then what? Then you want to keep multiple sets so you don’t lose anything.

Suppose you want to retain four weeks of data in each set. That means four full backups plus all their incrementals. That requires four sets (because each set gets its own backup) times the space of each individual set.

There is also the hidden overhead of metadata like block maps, indexes, and catalogs. These takes some space too, a few percent of your overall size per set, adding up when multiplied by multiple terabytes. Safety margin and growth are the last two buffers.

Next year, your data will grows. Your backup job might fail and require a retry consuming temporary space. Add a percentage for those unknowns to your calculator. Better off with empty space than a backup that fails.

Use the reference tables on the page to benchmark what you should of expect. This is a sanity check on what you enter. Predicting the future is always hard. This task in sizing your backup repository is no different. You’re making an estimate about the behavior of your data over time, months.

Fortunately, this math is done for you by the tool but it’s up to you to supply the context. Try restoring from points. Monitor disk use after several weeks time. Play with the dedup and compression ratios in the calculator until they reflects what actualy happens.

Your end result should be a plan that accommodates all of your history on a single drive. Start with a fear of running out of room, finish with a fit.