How many marshals do I need? A ratio method that works

1. Count decision points, not runners

A decision point is anywhere a runner could plausibly go the wrong way: a junction, a fork where two distances split, a turnaround, a gate, a path that continues straight when the route turns. Walk or drive the route in the direction of travel and list them. That list, not your entry cap, is the foundation of your marshal number.

2. Apply a category budget to each point

Assign people by what the position demands rather than a flat rate:

• Simple decision point, traffic-free: 1 marshal.
• Decision point with live traffic or poor sight lines: 2 marshals, so one always faces vehicles.
• Road crossing: 2 minimum, 3 where the field bunches early in the race.
• Distance split (10k right, half left): 2, plus clear signage — this is the single most common wrong-turn incident.
• Aid station: 2 for under 200 runners, 4–6 for a large field or a station serving multiple passes.
• Start/finish: a crew of 6–10 covering funnel, timing, bag drop, water and results.
• Sweeper: 1 per race distance, so you can declare the course clear.

3. Add cover for passes, not just points

On a lapped or out-and-back course, one physical position may be worked for three or four hours as different waves pass. That is a shift problem, not a headcount problem: either double-crew and rotate, or accept a long shift and say so in the brief. Count passes per point when you plan, or you will staff hour one properly and hour four not at all.

4. Add 10–15% for no-shows

Across UK community events, marshal no-show rates of around one in ten are normal, and higher in bad weather or when volunteers were recruited more than two months out with no contact since. Build the spare in deliberately and place them at the start, where they can be redeployed, rather than assigning them to a position you would then have to backfill.

5. Worked examples

Same method, three courses:

• Urban 5k, 300 runners, 6 decision points, 2 crossings: 6 + 4 + start/finish crew 8 + sweeper 1 + 2 spare ≈ 21 marshals.
• Half marathon, 800 runners, 14 decision points (2 with traffic), 3 crossings, 3 aid stations: 16 + 6 + 12 + start/finish 10 + sweeper 1 + 5 spare ≈ 50.
• 100km trail ultra, 200 runners, 22 decision points, 8 aid stations across 18 hours: 22 + 32 (crewed and rotated) + start/finish 8 + 2 sweepers + 8 spare ≈ 72 volunteer slots across multiple shifts.

6. Then check the number against your recruitment reality

If the method says 50 and you can realistically get 35, do not silently thin every position. Decide explicitly what you will do instead: signage plus a marshal at the split rather than at every junction, a shorter course, or a later cut-off. A documented decision is defensible; an accidental gap is not.

7. Keep the count tied to the map

The reason marshal numbers drift is that the count lives in a spreadsheet and the course lives in a map, and they stop agreeing. Keep positions, headcount and people in one place so a change to the route changes the number automatically. That is exactly what mrshl does: every point on the course carries its own shifts and required headcount, and anything short of people shows as a gap.