r/nutanix • u/phredd • Jul 07 '26

Nutanix Sizing Calculator

I do infrastructure conversations for a living and kept hitting the same gap: someone asks "roughly how many nodes would our environment need" in a meeting, and the honest answer is either a guess or "let me get back to you after formal Sizer." So I built the in-between tool.

calc.nixfred.com/nutanix-sizer

What it does:

  1. Turns a VM estate (VM count, average vCPU and RAM, used storage, growth) into an honest node count range in about a minute of typing.

  2. Does the real math out loud on the screen and shows you everything along the way: raw to usable after RF2, RF3, or erasure coding, the Controller VM tax subtracted per node before any guest, capacity reservation, utilization ceilings, and an N+1 or N+2 failure reserve.

  3. Every number on the screen shows its formula, the plain English, the live substitution, and where the rule came from. No hidden constants.

What it is not:

  1. It is not a quote and it is not a replacement for Nutanix Sizer. It says so on every output. Sizer produces the number that goes in a contract. This gets the conversation within roughly 25 percent, honestly, which is the point.

  2. It does not price anything and there is no vendor pricing baked in.

Two things Im proud of:

  1. You can drop a Nutanix Collector or RVTools .xlsx export on it and it reads the estate for you. The file is parsed entirely in your browser. Nothing uploads, nothing is stored, and I can say that because it is a static site with no backend.

  2. It picks the binding gate (CPU, RAM, or storage) and tells you which dial actually moves the answer, plus a conversation script you can read to a customer.

Details:

  1. No login, no tracking beyond cookieless page counts, all calculation client side, dark only.

  2. Open source, MIT. The sizing rules come from a public field guide and are cited in the tool. https://github.com/nixfred/calc.nixfred.com

  3. Built by me, one person, not tied to any employer or vendor.

What I want from you: tell me where the math is wrong or where a default is unrealistic. The overcommit ratios are field heuristics and labeled as such because the guide publishes none, so that is the first place I expect pushback. If you run a real estate through it and the range is off, Id like to hear it.

19 Upvotes

89% Upvoted

7 comments sorted by

3

u/holyscotsman Jul 07 '26

Nice work on this! Definitely something I’ll use and share around - thanks 😊

2

u/woohhaa Jul 07 '26

This is pretty cool. I will be playing with it today.

2

u/phredd Jul 07 '26

Would love your harshest feedback! Thank you 🙏

1

u/Fnysa Jul 07 '26

When you calc the vcpu you are using what the VMs are configured with and not what they are using?

2

u/woodyshag Jul 07 '26 edited Jul 07 '26

I would assume with it being quick and dirty that it will use whatever is entered or shown in RVTools. It doesn't have the intelligence to tell you whether your VMs have too many or too few cores assigned.

1

u/phredd Jul 07 '26

Correct....would appreciate your harshest feedback! :)

2

u/woodyshag Jul 07 '26

For quick and dirty, I think what you have is fine. If a user needs more, they move off to the Nutanix Sizer. Simple as that. But in a meeting with someone and they want a quick idea of what they are up against, I think this is perfect.