STEM
FermiForge
How many jelly beans fill that jar? How many breaths do you take in a day? You can guess almost anything — to within a power of ten — by breaking it into small pieces you CAN guess and multiplying. Meet Chunk, Bound, Round, Sanity and Unit, predict the order of magnitude, then watch your estimate land right next to the real answer. Real, tiny, deterministic maths — no calculator, no internet. Ages 9–14.
▶ Play it nowBuilt for sittings of about 20 minutes on the screen. That is our design budget, not a measurement.
Meet your mentor
Every Spark & Anvil app has a friendly mentor character that demonstrates, asks, and patiently scaffolds learning.
Mentored by Sanity
#5b57c9 Characters who teach
Meet the cast
FermiForge's crew ARE the five moves of a Fermi estimate — the cast IS the curriculum: each character's defining habit IS one step of the method. Chunk breaks an impossible question into two or three you can guess; Bound gives every piece a low guess AND a high guess (never a single number); Round keeps the figures friendly so the maths stays in your head; Unit keeps the labels straight so nothing multiplies wrong. Mentor Sanity asks the honest closing question — does this answer feel right, is it in the right ballpark — which is exactly why a low-and-high guess that brackets reality lands you within a power of ten. Nothing leaves the device.
Chunk
Breaks the impossible question into two or three small ones you can actually guess; nothing gets estimated until Chunk has split it up
Bound
Gives each piece a LOW guess and a HIGH guess — always a range, never a single number; the range is what pins the answer to a power of ten
Round
Keeps the numbers friendly, rounding to one clean figure so the whole estimate can be done in your head
Sanity
Asks the honest closing question — does this answer feel right? is it in the right ballpark? — the sanity check that turns a wild guess into a Fermi estimate
Unit
Keeps the labels straight — beans per layer, layers, breaths per minute — so the factors multiply into the right thing
What's inside
Learning goal
How many jelly beans fill that jar? How many breaths do you take in a day? You can guess almost anything — to within a power of ten — by breaking it into small pieces you CAN guess and multiplying. Meet Chunk, Bound, Round, Sanity and Unit, predict the order of magnitude, then watch your estimate land right next to the real answer. Real, tiny, deterministic maths — no calculator, no internet. Ages 9–14.
Mentored by Sanity — no data leaves the device.
How FermiForge handles your kid's data
- ✅ All progress, settings, and AI-generated content stays on the device
- ✅ No analytics, no tracking, no third-party SDKs
- ✅ Free — no ads, no in-app purchases
- ✅ No personal information collected from children — in line with COPPA (updated by the 2026 FTC amendments)
- ✅ No chat with strangers — play-together rooms use a short code and preset emotes, never typed messages