October 28, 2026
Model Railroad Turnout Numbers Explained: Angle, Length, and Space
Hobby articles / Model Railroads
By LootBandit
Browse the Model Railroad Control, Track, and Troubleshooting Guides collection.
A numbered model railroad turnout is generally named for the divergence at its frog: a No. 6 frog spreads one unit for every six units of forward travel, while a No. 4 spreads one unit for every four. A larger number represents a gentler frog angle. That does not mean every brand’s No. 6 turnout has exactly the same length, closure-rail shape, or crossover spacing. Use the manufacturer’s dimensioned drawing before cutting roadbed.
What the number actually measures
The frog is the crossing point where wheel paths intersect as one route diverges from another. The NMRA’s beginner’s glossary defines the turnout number as the ratio between forward distance and separation at the frog. For a simple mental model, a No. 6 means roughly six units along for one unit apart at that location.
This is a geometric ratio rather than an exact statement about curve radius. The rails leading to the frog and the transition after it determine how the complete turnout behaves. Some train-set switches are specified primarily by an equivalent curve radius instead of a frog number, making cross-brand comparisons especially tricky.
Compare three common choices
| Frog number | Divergence | Typical planning use |
|---|---|---|
| No. 4 | Relatively sharp | Compact industrial tracks and small yards where rolling stock permits |
| No. 6 | Moderate | Passing sidings, yards and many general-purpose routes |
| No. 8 | Gentler | Main-line movements or long equipment where space allows |
Those are planning tendencies, not minimum equipment-radius certifications. A long passenger car can still derail on a poorly aligned No. 8. A small switcher may run well on a No. 4 if all clearances, gauges and wheelsets agree.
Calculate the actual footprint with a paper template
Start with the available length between the planned turnout points and the platform or end of siding. Print or draw an accurately scaled template of the specific turnout. Mark its point end, frog, straight-route exit, and diverging-route exit. Lay out the intended second turnout or adjacent curved track and check whether both tracks meet at the same centerline separation.
For a crossover, test the complete arrangement, not just two individual switches. The S-bend created as a car moves from one parallel main to another can put opposing offsets into its couplers. The NMRA’s track-laying guide warns about abrupt S-curves, especially with body-mounted couplers and long cars.
Left and right turnouts
A left-hand turnout diverges left when viewed from its point end toward the frog, with the stock rails defining the approach. A right-hand turnout does the opposite. Be sure your plan uses the same viewing direction as the manufacturer’s diagram. Buying the opposite hand can move a siding or industry track toward the wrong benchwork edge.
Watch out for wye turnouts as well: both routes branch away from the approach centerline, so a wye is not simply an extra-compact version of a left or right turnout.
Electrical design is a separate choice
Frog number tells you nothing about whether the frog is insulated, powered, or switched. Product families may differ in point wiring, frog polarity, and motor compatibility. On DCC layouts, wiring a frog incorrectly can cause a short as wheels bridge mismatched polarities. Plan the electrical system from the manufacturer’s wiring sheet, not from a drawing that shows only the rails.
A useful selection workflow
- Choose the longest locomotive and car expected on the route.
- Compare their manufacturer-stated curve and turnout recommendations where available.
- Print full-size templates for the exact proposed switch models.
- Place two switches in the desired yard ladder or crossover and verify total length.
- Allow a straight or eased transition where opposing curves meet.
- Test free-rolling cars through every route before fixing the turnout to roadbed.
- Check the frog’s wiring and any required switch machine before final ballast.
The number is the start, not the answer
If you want to fit five industry spurs into a short shelf layout, No. 4 turnouts may look attractive on paper. But if you operate modern long freight cars or large steam, gaining a few inches of yard length can cost you dependable running. Conversely, fitting No. 8 turnouts everywhere can consume space without improving the operation of a tiny switching locomotive.
Choose a turnout by frog angle, complete footprint, equipment compatibility, and electrical features together. That combination is far more useful than treating a bigger number as automatically better.
