Max it out
Not in the market for a V02max test in a lab? Do your own field test. The two here yielded the most accurate estimates in a recent study.
Run as far as you can in 12 mins. Use GPS or run on a treadmill (at a 1% incline) to measure your distance. (22.35 x km covered) - 11.29 = your estimated V02 max*
1.5-mile run test
Run a 1.5-mile (2.4km) route as fast as you can. Pace wisely: runners often start distance-based tests faster, yielding a higher rate of perceived exertion (RPE). 483 ÷ time + 3 = your estimated V02 max