US Navy method, using log10 of circumference measurements
Men: %BF = 495 ÷ (1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450.
Body fat distribution patterns differ by sex, so the Navy method uses a hip measurement for women in addition to neck and waist.
It's a reasonable estimate for general tracking but less precise than DEXA scans or hydrostatic weighing.