Model Scale Calculator
HO, N, O, 1:35, 28mm & more
Free · Designed for iPad. Not verified for macOS.
Pick a scale, type a dimension, read the answer as you type. Real to model, model to real, and “what scale is this?”
A scale converter for people who build models.
Pick a scale — HO, N, O, 1:35 armour, 28mm heroic, 1/4" = 1' — type a dimension, and read the answer as you type. Free, offline, no account, no ads.
THREE ANSWERS, ONE SCREEN
• Real → model — how big is a 40-foot boxcar in HO?
• Model → real — this part measures 92 mm; what is that full size?
• What scale is this? — give a real length and the model length it has to come out at, and get the ratio.
COMPARE ACROSS SCALES
A second view takes one measurement and shows it in every scale in a hobby group at once — model railway gauges, military armour, aircraft, tabletop miniatures — with a proportional bar per row so you can judge the sizes by eye instead of reading numbers.
UNITS HOBBYISTS ACTUALLY TYPE
It parses what you would write on a workbench note: 250mm, 2.5 cm, 5' 6", 5ft 6in, 1 1/2", 3/4", 1-1/2". Feet-and-inches and fractional inches are first-class output formats, not an afterthought — fractions come back as fractions, rounded to the precision you choose.
SCALES INCLUDED
• Model railways — Z, N, TT, HO, OO, S, O, G and more
• Military and armour — 1:16, 1:35, 1:48, 1:72
• Aircraft — 1:32, 1:48, 1:72, 1:144
• Cars — 1:18, 1:24, 1:43, 1:64
• Tabletop and wargaming — 15mm, 28mm heroic, 32mm, 54mm
• Architecture — imperial drawing scales like 1/4" = 1' and metric 1:50, 1:100
• Any custom ratio you type
WORKS COMPLETELY OFFLINE
No account, no sign-in, no sync, no paywall and no advertising. Every calculation happens on your device, and nothing you type is ever sent anywhere. The only thing the app ever sends is anonymous usage data — which scales and modes get used — and you can switch that off in Settings.
For model railroaders, scale modellers, miniature painters, RC builders, dollhouse makers, architects and anyone who has ever stood in a hobby shop doing long division on their phone.
Ratings & Reviews
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The developer, Harbor Apps LLC, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Linked to You
The following data may be collected but it is not linked to your identity:
- Usage Data
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Harbor Apps LLC
- Size
- 4.2 MB
- Category
- Utilities
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - iPad
Requires iPadOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- Copyright
- © 2026 Rhett Owen