/diy/ - Do It Yourself

I have these toroidal cores that I want to know the maximum amp-turns of, pic related. They're 35OD x 21ID x 13H (mm) toroids. The webpage refers to the ferrite material as "Toroid L8". The chinglish datasheet's only reference to magnetic field is this "Bms" value, with 2500 (gauss?) and 20Oe values.

20 oersted is 1592 amperes per metre, while 2500 gauss is 0.25 tesla. I think this oersted / amps per metre value is what I want, as it's the H field you put into the core as opposed to the B field you get out. But this H field strength and the magneto-motive-force F I want are related to one another with the equation F = H*L, where L is the effective length of the solenoid. The effective length of this toroid is probably 88mm or 0.088m, so F = 1592 * 0.088 = 140 amp turns. This sounds sensible I guess, but the fact that this depends on the length of the toroid but not the cross-sectional area feels really wrong to me.

Does anyone here understand magnetics enough to tell me what the fuck I'm doing wrong?