Make the distance familiar
A 100 km length contains 1,000 straight 100 m sections. Picture a marked 100 m sprint straight repeated end to end, rather than a whole stadium lap.
Work it out, one step at a time
Turn kilometres into metres
100 × 1,000 = 100,000 m
One kilometre contains 1,000 metres. The length stays the same.
Choose a speed, then find the time
100 km ÷ 100 km/h = 1 h
At a chosen constant 100 km/h, it takes about 1 hours. This is a calculation with no stops; hills, traffic and real journey conditions are not included.
What if the speed doubles?
For the same distance and constant speed, time halves. For example, 10 km takes 2 hours at 5 km/h but 1 hour at 10 km/h.
The distance is this page’s chosen input. The speed is a teaching assumption. Time = distance ÷ speed.
Build a scale modelChoose two references and change the model size.
Build a scale model of any two lengths
Choose from all 71 Macro and 54 Micro references, or enter your own length. Set B’s model length and see A change on the same fixed metre ruler. The bars represent the stated lengths, including their different measurement definitions.
- Length ratio A / B
- Model length B
- Calculated model length A
A · Chosen distance A
100 km
A chosen input length, not a new measurement of a reference.
User / page input
The ratio follows this input assumption.
Definition and evidence reviewOriginal sourceB · Marathon
42.195 km
Official marathon race distance, 42.195 km.
Source claim checked
A standardized course length; course certification and an athlete’s path require separate measurement.
Definition and evidence reviewOriginal sourcemodel A = (A / B) × model B
This calculator uses the existing journey comparison inputs. Review-pending or conceptual entries remain illustrative inputs here; the public reviewed dataset keeps their numeric values withheld. Radius, height, diameter and experimental bound keep their individual definitions.
A map scale changes when the image is resized
Assume a map has uniform scale 1:1,000,000. One centimetre represents 10 km, so a 100 km segment occupies 10 cm: 100 × 100,000 cm / 1,000,000. This idealized map exercise isolates scale from projection effects.
Enlarge both dimensions to 125% when printing. The same segment now measures 12.5 cm; the effective scale becomes 1:(1,000,000 / 1.25) = 1:800,000. Applying the old numerical scale to the enlarged image would overestimate the segment by 25%.
Read the scale bar and the measurement precision
A scale bar enlarged together with the map retains its relative meaning: its drawn length changes with the features. A separate “1:1,000,000” label needs updating. At the original scale, a 1 mm difference in ruler placement corresponds to 1 km on the ground. This is a measurement-sensitivity example; real map accuracy also depends on its data and projection.
Closest ScaleTrip references
Page distance: 100 km
- Seoul–DaejeonReference measurement: Distance · 140 km
Ratio (page distance ÷ reference): ≈ 0.71×The approximate straight-line distance between Seoul and Daejeon.
- Taiwan widthReference measurement: Length · 144 km
Ratio (page distance ÷ reference): ≈ 0.69×A representative east-to-west width across Taiwan.
- Channel TunnelReference measurement: Length · 50.45 km
Ratio (page distance ÷ reference): ≈ 1.98×The rail tunnel linking England and France beneath the sea.